use command 'blkid' instead of 'mount' to check the filesystem type

The options "--guess-fstype" was removed from the mount command [1].
Commands "fsck -N" and "file -sL" were also tested but their output are
not consitent between filesystems. 'blkid' finally seems to be the best candidate
to replace 'mount' and this utility is also present in the standard
package util-linux.

This patch fix the following bug https://projects.puppetlabs.com/issues/19410

[1] http://git.kernel.org/?p=utils/util-linux/util-linux.git;a=commit;h=0377ef91270d06592a0d4dd009c29e7b1ff9c9b8
Merge pull request #23 from mbornoz/master

use 'blkid' instead of 'mount' to check the filesystem type