When upgrading from one Ceph version to another, the new image to
upgrade to can take a long time to pull in some cases before the upgrade
can even begin. For example, some ceph-ci images regularly take 6+
minutes to pull, which exceeds the timeout waiting for mons to be ready.
Extend the timeout for mons to account for these cases.
Signed-off-by: Blaine Gardner <blaine.gardner@ibm.com>