[pcp_metrics] Create a usroverlay instead of remounting /usr

Remounting the `/usr` directory on coreos nodes was failing on
newer crc releases because `/usr` is read-only. This changes the remount
to use the `rpm-ostree usroverlay` command to create a temporary
writable layer instead.

Data written to this overlay will not persist between boots.

Signed-off-by: Michael Burke <michburk@redhat.com>

Author: michburk

roles/pcp_metrics/tasks/coreos.yaml

@@ -11,12 +11,10 @@
 - name: Setup repositories for PCP
   ansible.builtin.include_tasks: repo.yml
 
-- name: Make /usr writable
+- name: Create an writable, ephemeral /usr overlay
   become: true
-  ansible.posix.mount:
-    path: /usr
-    state: remounted
-    opts: rw
+  ansible.builtin.command:
+    cmd: rpm-ostree usroverlay
 
 - name: Create required directory
   become: true