fix: app cmd parsing, usage & tests

Note: the integration tests don't work due to ValidateApp still
attempting to validate the host key for the test app which doesn't
exist. This will be fixed in a future commit.

tests/integration/cmd.sh

@@ -0,0 +1,14 @@
+#!/bin/bash
+
+source ./testfunctions.sh
+source ./common.sh
+
+create_server_app_recipe
+
+run_test '$ABRA app cmd foo.com test --local'
+
+run_test '$ABRA app cmd foo.com test --local -- foo'
+
+run_test '$ABRA app cmd foo.com test --local -- foo bar baz'
+
+clean_server_app_recipe