rgw: change watch init ordering, don't distribute if can't

Backport: dumpling

Moving back the watch initialization after the zone init,
as the zone info holds the control pool name. Since zone
init might need to create a new system object (that needs
to distribute cache), don't try to distribute cache if
watch is not yet initialized.

Reviewed-by: Sage Weil <sage@inktank.com>
Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>