Update Testing section in Makefile

This commit applies some conventions to the targets and documentation in
the testing section:

 - Use single spaces before help text (results in shorter lines)
 - Clarify build and push image targets for content
 - Add documentatin for prep-e2e
 - Add e2e target to the testing section
 - Fix the must-gather target by adding push-must-gather-image

Fixes #159

Makefile

@@ -411,7 +411,7 @@ image: ## Build the operator image.
 images: image bundle-image  ## Build operator and bundle images.
 
 .PHONY: images-extra
-images-extra: openscap-image e2e-content-images  ## Build the openscap and test content images.
+images-extra: openscap-image build-e2e-content-images  ## Build the openscap and test content images.
 
 .PHONY: build
 build: generate fmt vet test-unit ## Build the operator binary.
@@ -546,24 +546,24 @@ catalog-push: ## Push a catalog image.
 ##@ Testing
 
 .PHONY: test-unit
-test-unit: fmt ## Run the unit tests
+test-unit: fmt ## Run the unit tests locally.
 ifndef JUNITFILE
 	@$(GO) test $(TEST_OPTIONS) $(PKGS)
 else
 	@set -o pipefail; $(GO) test $(TEST_OPTIONS) -json $(PKGS) --ginkgo.noColor | gotest2junit -v > $(JUNITFILE)
 endif
 
 .PHONY: test-benchmark
-test-benchmark: ## Run the benchmark tests -- Note that this can only be ran for one package. You can set $BENCHMARK_PKG for this. cpu.prof and mem.prof will be generated
+test-benchmark: ## Run the benchmark tests against a single package using $BENCHMARK_PKG. CPU and memory output will be in cpu.prof and mem.prof files, respectively.
 	@$(GO) test -cpuprofile cpu.prof -memprofile mem.prof -bench . $(TEST_OPTIONS) $(BENCHMARK_PKG)
 	@echo "The pprof files generated are: cpu.prof and mem.prof"
 
 .PHONY: e2e
-e2e: e2e-set-image prep-e2e
+e2e: e2e-set-image prep-e2e ## Run end-to-end tests against a deployed operator.
 	@CONTENT_IMAGE=$(E2E_CONTENT_IMAGE_PATH) BROKEN_CONTENT_IMAGE=$(E2E_BROKEN_CONTENT_IMAGE_PATH) $(GO) test ./tests/e2e $(E2E_GO_TEST_FLAGS) -args $(E2E_ARGS) | tee tests/e2e-test.log
 
 .PHONY: prep-e2e
-prep-e2e: kustomize
+prep-e2e: kustomize ## Build kustomize resources and deploy the operator.
 	rm -rf $(TEST_SETUP_DIR)
 	mkdir -p $(TEST_SETUP_DIR)
 	$(KUSTOMIZE) build config/no-ns | sed -e 's%$(DEFAULT_OPERATOR_IMAGE)%$(OPERATOR_IMAGE)%' -e 's%$(DEFAULT_CONTENT_IMAGE)%$(E2E_CONTENT_IMAGE_PATH)%' -e 's%$(DEFAULT_OPENSCAP_IMAGE)%$(OPENSCAP_IMAGE)%'  > $(TEST_DEPLOY)
@@ -579,10 +579,10 @@ e2e-set-image: kustomize
 endif
 
 .PHONY: e2e-cluster
-e2e-cluster: image-to-cluster e2e  ## Builds and pushes the operator and openscap images to the cluster registry, and starts an e2e test suite against the cluster images.
+e2e-cluster: image-to-cluster e2e ## Builds and pushes the operator and openscap images to the cluster registry, and starts an e2e test suite against the cluster images.
 
 .PHONY: image-to-cluster
-image-to-cluster: image openscap-image namespace openshift-user  ## Builds and pushes the operator and openscap images to the cluster registry.
+image-to-cluster: image openscap-image namespace openshift-user ## Builds and pushes the operator and openscap images to the cluster registry.
 	@echo "Temporarily exposing the default route to the image registry"
 	@oc patch configs.imageregistry.operator.openshift.io/cluster --patch '{"spec":{"defaultRoute":true}}' --type=merge
 	@echo "Pushing image $(OPERATOR_IMAGE) to the image registry"
@@ -596,20 +596,24 @@ image-to-cluster: image openscap-image namespace openshift-user  ## Builds and p
 	$(eval IMG = image-registry.openshift-image-registry.svc:5000/openshift/$(APP_NAME):$(TAG))
 	$(eval OPENSCAP_IMAGE = image-registry.openshift-image-registry.svc:5000/openshift/$(OPENSCAP_NAME):$(OPENSCAP_TAG))
 
-.PHONY: e2e-content-images
-e2e-content-images:  ## Build the e2e-content-image
+.PHONY: build-e2e-content-images
+build-e2e-content-images: ## Build content image for end-to-end testing.
 	RUNTIME=$(RUNTIME) images/testcontent/broken-content.sh build ${E2E_BROKEN_CONTENT_IMAGE_PATH}
 
-.PHONY: push-e2e-content
-push-e2e-content: e2e-content-images  ## Build and push the e2e-content-images
+.PHONY: push-e2e-content-images
+push-e2e-content-images: build-e2e-content-images ##Push the content image for end-to-end testing to an image repository.
 	RUNTIME=$(RUNTIME) images/testcontent/broken-content.sh push ${E2E_BROKEN_CONTENT_IMAGE_PATH}
 
-.PHONY: must-gather-image
-must-gather-image:  ## Build the must-gather image
+.PHONY: build-must-gather-image
+build-must-gather-image: ## Build the must-gather image.
 	$(RUNTIME) build -t $(MUST_GATHER_IMAGE_PATH):$(MUST_GATHER_IMAGE_TAG) -f images/must-gather/Dockerfile .
 
+.PHONY: push-must-gather-image
+push-must-gather-image: ## Push the must-gather image to an image repository (default: quay.io/compliance-operator/must-gather).
+	$(RUNTIME) push ${MUST_GATHER_IMAGE_PATH}:${MUST_GATHER_IMAGE_TAG}
+
 .PHONY: must-gather
-must-gather: must-gather-image must-gather-push  ## Build and push the must-gather image
+must-gather: must-gather-image must-gather-push ## Build the must-gather image and push it to an image repository (default: quay.io/compliance-operator/must-gather).
 
 ##@ Release