Use .env as dev_mode flag rockstor#2939

Rely on the DJANGO_DEBUG env variable to set DEBUG boolean that will in
turn decide the installation of the dev group dependencies (includes
the Django debug toolbar) as the appearance of the toolbar in the UI.

Leave commented (= unset) by default to keep the default build NOT in
the dev mode.

.env

@@ -12,3 +12,4 @@ PASSWORD_STORE_DIR=/root/.password-store
 
 # Django
 DJANGO_SETTINGS_MODULE=settings
+#DJANGO_DEBUG=True

build.sh

@@ -2,11 +2,6 @@
 # exit on error
 set -o errexit
 
-DEV_MODE=0
-if [ "$1" = "--dev" ]; then
-    DEV_MODE=1
-fi
-
 # Install Poetry, a dependency management, packaging, and build system.
 # Uninstall legacy/transitional Poetry version of 1.1.15
 PATH="/root/.local/bin:$PATH"  # ensure legacy path.
@@ -54,8 +49,8 @@ poetry --version >> poetry-install.txt
 poetry self show plugins >> poetry-install.txt
 # /usr/local/bin/poetry -> /opt/pipx/venvs/poetry
 
-if [ $DEV_MODE -eq 1 ]; then
-	echo "Install djdt."
+if [ "$DJANGO_DEBUG" = "True" ]; then
+	echo "Install Django Debug Toolbar."
   poetry install -vvv --no-interaction --no-ansi --with dev >> poetry-install-dev.txt 2>&1
 else
 	echo "Normal install."