Restore selinux context on swift mount

Mounting devices without specifying or restoring context ends up with
default context file_t assigned for swift paths. On selinux systems it
is nice to at least try to preserve predefined contexts on paths.

Change-Id: I9b68c04cb0d4ee72c074e514db7141c3c077c978
Closes-Bug: rhbz#1095503
Closes-Bug: #1320853
(cherry picked from commit 9ca38e7e442ac8e59bf21c78a43feea5c025501a)
Merge "Restore selinux context on swift mount" into stable/icehouse