fabfile: install libxfs

Ceph now depends on libxfs (xfslibs-dev .deb, xfsprogs-devel .rpm).
Install it.

Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Merge pull request #11 from ceph/wip-libxfs

fabfile: install libxfs