LU-6013 utils: fix off-by-one error

Code that generates path to mount.lustre_osd had an off-
by-one error when checking to ensure it did not exceed
MAX_PATH.

Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Change-Id: Id331c7cb45da4a770861ff85eff6387edbf01e69
LU-6013 utils: add new binary to .gitignore

Added new binary, mount.lustre_osd, to
lustre/utils/.gitignore

Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Change-Id: Ie54751e725a354537f40ad099c17d757ea5c009b
LU-6013 utils: improve mount_lustre*.c comments

Improve comments in code explaining relationship of client and
server mount helpers, mount_lustre_*.c

Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Change-Id: I8b41ad0f7b1a8ba2b887528825078143e5522a1e