EX-4006 pcc: improve pcc-detach and man pages

EX-4006 pcc: improve pcc-detach and man pages

Improve "lfs pcc detach_fid" to have a "--mnt|-m" option to match
the corresponding option for "lfs pcc attach_fid".  There isn't
any reason that they should be different.

Separate lfs-pcc-attach.1 and lfs-pcc-detach.1 from the
lfs-pcc.1 man page and improve descriptions of these commands.
Add links for lfs-pcc-attach_fid.1 and lfs-pcc-detach_fid.1.

Test-Parameters: trivial testlist=sanity-pcc
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Ieff40b7b133aef64200a9a3f6c1a948d7c3ebbe5
Reviewed-on: https://review.whamcloud.com/45178
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Yingjin Qian <qian@ddn.com>
Reviewed-by: Feng, Lei <flei@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>