[FIX] Fix flaky embargo tests

**ISSUE**
The embargo specs fail intermittently when run in the full suite.

**DIAGNOSIS**
Depending on the randomized test order, the admin tests may run
before the regular user tests. In some test orders, the admin
user may remain logged in while the tests for regular users are run
resulting in admin-only data being rendered in the views.

**FIX**
Explicitly log out any user from a previous test when testing
regular or unauthenticated user views.

spec/system/embargo_show_spec.rb

@@ -45,6 +45,7 @@
   end
 
   scenario "base etd has expected embargo values after creation", :aggregate_failures do
+    logout
     expect(etd.degree_awarded).to eq nil
     expect(etd.embargo.embargo_release_date).to eq many_years_from_today
     expect(etd.embargo_length).to eq "6 months"
@@ -121,6 +122,7 @@
     etd.reload # to clear cached data in memory after approval & graudation processes
 
     # viewed by any user - logged in or not
+    logout # ensure we're not still logged in as an admin from another test
     visit("/concern/etds/#{etd.id}")
     expect(page).to have_content "Abstract"
     expect(page).to have_content "This abstract is under embargo until #{formatted_embargo_release_date(etd)}"