LU-15548 osd-ldiskfs: hide virtual projid xattr

LU-15548 osd-ldiskfs: hide virtual projid xattr

Add tunable enable_projid_xattr to hide the virtual
project ID xattr by default.

Change-Id: I21263d91599f9e2d5850cb9d94a8b6df90c8443c
Test-Parameters: trivial testlist=conf-sanity env=ONLY=131
Test-Parameters: testlist=sanity env=ONLY=904
Signed-off-by: Li Dongyang <dongyangli@ddn.com>
Reviewed-on: https://review.whamcloud.com/46900
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Li Xi <lixi@ddn.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>