mds: Adjust replay state changes and options parsing.

mds: Adjust replay state changes and options parsing.

The MDS used to interpret g_conf.id as a rank. It no longer does
so and requires that standby ranks/names be set via the g_conf options,
or else along with the replay command in the CLI. Remove the MDS versions
of standby_for_[rank|name] and just use the ones in g_conf for simplicity.

However, the MDS only looks at the rank when switching to standby;
making names usable will require an update to the MDSMonitor code to
plug in ranks from names.

Signed-off-by: Greg Farnum <gregory.farnum@dreamhost.com>