ceph-osd: get full link path when testing if a partition

ceph-osd: get full link path when testing if a partition

This allows us to test devices set with persistent naming such as
/dev/disk/by-*
When registering devices we can use persisent (/dev/disk/by-*) or
non-persistent (/dev/sd*). Both declarations are supported by
ceph-ansible. There was just two tasks that were not compatible with
this. Since we support using partitions directly we need to test that
because the device activation will be different. To test if the device
is a partition we use a regular expression which wasn't compatible with
the persistent device naming format (/dev/disk/by-*).

This commit solves this issue by reading the path of the symlink since
devices like /dev/disk/by-* are symlinks to devices like /dev/sd*

Signed-off-by: Sébastien Han <seb@redhat.com>