parse_opts determines whether starting service

Determine in parse_opts whether we are starting a target service
or starting a lustre client.  Pass that information back to the
caller.
refactor mount.lustre to use flag starting_client

Refactor mount.lustre to use the flag starting_client set by
parse_opts instead of doing string comparison each time it must
call a function that is only relevant to starting a target
service.

Should be no change to functionality.