LUDOC-371 config: Add lctl 'clear_conf' documentation.

LUDOC-371 config: Add lctl 'clear_conf' documentation.

The new lctl command "clear_conf" is added to allow
administartors to clear configuration files by removing
SKIP records. The old configuration files are backed up.

Signed-off-by: Arshad Hussain <arshad.hussain@seagate.com>
Signed-off-by: Vladimir Saveliev <vladimir.saveliev@seagate.com>
Change-Id: Iacc52127b0b93e736430cc13d4c9c852eac8dc2d
Seagate-bug-id: MRP-2091
Reviewed-on: https://review.whamcloud.com/26083
Tested-by: Jenkins
Reviewed-by: Arshad Hussain <arshad.super@gmail.com>
Reviewed-by: Joseph Gmitter <jgmitter@whamcloud.com>