cluster: remove extra write_file argument

http://tracker.ceph.com/issues/10170 Fixes: #10170

Signed-off-by: Loic Dachary <ldachary@redhat.com>
cluster: add owner argument to write_file

The misc.sudo_write_file now supports the optional owner argument, add
support for it.

Signed-off-by: Loic Dachary <ldachary@redhat.com>
Merge pull request #366 from dachary/wip-10170-write-file

fix Cluster::write_file extra argument & support owner