Nova/Glance: Mount nfs device with puppet

With 'ensure => present' in types::nfs we have only fstab configured.
Change it to 'ensure => mounted' it mount the device during puppet agent.

Signed-off-by: Dimitri Savineau <dimitri.savineau@enovance.com>
Merge pull request #676 from dsavineau/fix-nfs-mount

Nova/Glance: Mount nfs device with puppet