Fix: Repair "uninstall_all"

Refs: #2209
- The "uninstall_all" was broken during development of #2120,
to fix the issue a failure when there is no CNF to uninstall
has been relegated to a warning and exit 1 was removed.
- Two spec tests have been added to avoid this scenario
in the future.
- Additionally some renaming was left-over from #2184 that
was resolved.

Signed-off-by: svteb <[email protected]>

spec/setup_spec.cr

@@ -101,7 +101,7 @@ describe "Installation" do
       (/A CNF is already set up. Setting up multiple CNFs is not allowed./ =~ result[:output]).should_not be_nil
     ensure
       result = ShellCmd.cnf_uninstall()
-      (/All CNF deployments were uninstalled/ =~ result[:output]).should_not be_nil
+      (/CNF uninstallation skipped/ =~ result[:output]).should_not be_nil
     end
   end