Speed up the /plans/provision/container plan (#3418)

While the rest of the full tmt plans take about 20 minutes,
`/plans/provision/container` takes over an hour to complete. Let's
speed up the testing by running the install and ansible tests
separately as they take the most time.

Author: psss

plans/provision/container.fmf

@@ -25,3 +25,15 @@ environment:
     PROVISION_HOW: container
 
 enabled: true
+
+/install:
+    discover+:
+        test: install
+
+/ansible:
+    discover+:
+        test: ansible
+
+/the-rest:
+    discover+:
+        exclude: (install|ansible)