RGW - Allow starting RGW/dbstore without connecting to Mons

RGW - Allow starting RGW/dbstore without connecting to Mons

DBStore, and some other Stores like Motr, don't need to connect to the
Mons to work.  However, startup automatically connects to the mons.
There's provision to not connect, but the split isn't quite right.  We
need to call global_pre_init() to get config from the file, to determine
which store to start, but we then need to decide before calling
global_init() whether the configured store needs to connect to the mons.

This requires a slight change to global_init() to set no_mon_config from
the new flags.

Signed-off-by: Daniel Gryniewicz <dang@redhat.com>