Highlight uncommitted changes in version

If there are uncommitted changes in the app repository when building,
then append `_uncommitted_<random>` to it to distinguish the image
from one built from a clean checkout.

Also change the version used when renaming a container on redeploy to
distinguish and explain the version suffixes.

test/integration/deploy_test.rb

@@ -110,7 +110,7 @@ class DeployTest < ActiveSupport::TestCase
     end
 
     def latest_app_version
-      deployer_exec("cat version", capture: true)
+      deployer_exec("git rev-parse HEAD", capture: true)
     end
 
     def assert_app_version(version)