tests/installed: Disable all rpmmd repos

For the same reason we do in the rpm-ostree tests.  This also
made sure the test run worked when I was offline on a plane.

Closes: #1583
Approved by: jlebon

tests/installed/tasks/disable-all-rpmmd-repos.yml

@@ -0,0 +1,5 @@
+- name: Disable all rpmmd repos
+  shell: |
+    for x in /etc/yum.repos.d/*.repo; do
+      sed -i -e 's,^enabled=,enabled=0,g' $x
+    done