LU-6013 utils: improve comments

Make comments clearer, surrounding new code to exec() mount.lustre_osd
when not a client mount.

Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Change-Id: Ic512aa58e20b79b5d6a3407887abed73df59bee4
LU-6013 utils: more explicit return code check

Check specifically for negative return code (error)
after call into handle_server_start()

Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Change-Id: I0eb8d451ace002c324f929dd43daa67efceacf09
LU-6013 utils: remove dead code from mount_lustre*.c

Remove client-only code from mount_lustre_osd.c, and
server-only code from mount_lustre.c.

In both cases, the only code removed is that directly
identified by tests for ":/" in the mo_source
string, or code called directly by that code.

Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Change-Id: I71cf96d0b303f31a9910abf6aa45f59853706a33