mon: change mon_globalid_prealloc to 10000 (from 100)

mon: change mon_globalid_prealloc to 10000 (from 100)

100 ids (session 100 authentications) can be consumed quite quickly if
the monitor is being queried by the CLI via scripts or on a large cluster,
especially if the propose interval is long (many seconds).  These live in
a 64-bit value and are only "lost" if we have a mon election before they
are consumed, so there's no real risk here.

Backport: giant, firefly
Reviewed-by: Joao Eduardo Luis <joao@redhat.com>
Signed-off-by: Sage Weil <sage@redhat.com>