LU-930 doc: improve mount.lustre.8 option descriptions

LU-930 doc: improve mount.lustre.8 option descriptions

Add the "mgssec=<flavor>" mount option for SSK and Kerberos.
Add the "lazystatfs" and "nolazystatfs" mount options.
Add a description of mount-by-label and mount-by-UUID, with caveats.
Improve the description of the "mgsnode" parameter.
Improve the description of the "flock" and "noflock" options.
Move the "acl" and "noacl" mount options from the client to the
server section, since they've been long deprecated on the client.
Remove trailing whitespace.

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I2203df49270ff1f18b7bed20042eafff893ebbe5
Reviewed-on: https://review.whamcloud.com/25679
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>