test: get latest via helper

tests/integration/app_deploy.bats

@@ -108,8 +108,6 @@ teardown(){
 
 # bats test_tags=slow
 @test "deploy latest commit if no published versions and no --chaos" {
-  latestCommit="$(git -C "$ABRA_DIR/recipes/$TEST_RECIPE" rev-parse --short HEAD)"
-
   _remove_tags
   _wipe_env_version
 
@@ -117,7 +115,7 @@ teardown(){
   run $ABRA app deploy "$TEST_APP_DOMAIN" \
     --no-input --no-converge-checks --offline
   assert_success
-  assert_output --partial "$latestCommit"
+  assert_output --partial "${_get_head_hash:0:8}"
 }
 
 # bats test_tags=slow