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/resources/testapp/foo.com.env

@@ -0,0 +1 @@
+TYPE=test

tests/resources/testapp/testapp

@@ -0,0 +1 @@
+.

tests/resources/testrecipe/abra.sh

@@ -0,0 +1,5 @@
+test(){
+  echo "1: $1"
+  echo "2: $2"
+  echo "all: $@"
+}

tests/resources/testrecipe/compose.yml

@@ -0,0 +1,5 @@
+---
+version: "3.8"
+
+services:
+  app: []