Various ceph-related tasks were missing a 'become' that would allow them
to work as a non-root user. This seems to only cause a problem after an
initial deployment, perhaps due to the recursive ownership & permissions
changes at the end of the ceph.yml and external_ceph.yml files.
This change adds the necessary becomes.
Change-Id: I887c7b3bdef49db1dd1bf9e5bdbf5dc47b7f41af
Closes-Bug: #1795125