s3-printing: reload shares after pcap cache fill

s3-printing: reload shares after pcap cache fill

Since commit eada8f8a, updates to the cups pcap cache are performed
asynchronously - cups_cache_reload() forks a child process to request
cups printer information and notify the parent smbd on completion.

Currently printer shares are reloaded immediately following the call to
cups_cache_reload(), this occurs prior to smbd receiving new cups pcap
information from the child process. Such behaviour can result in stale
print shares as outlined in bug 7836.

This fix ensures print shares are only reloaded after new pcap data has
been received.

Pair-Programmed-With: Lars Müller <lars@samba.org>
(cherry picked from commit a8a01e4a3dcafd97372021d0d6f859fd3a69235f)