Fixed parted utils for newer parted

In the newer parted, the new flag 'esp' is added to the 'boot' flag on all
partitions.

Also fixed issue where we returned the trailing commas when a partition had
more than one flag.

Change-Id: I21b5842abb03f08b15b067c0c6e5889091bcdc5d
Signed-off-by: David Caro <dcaroest@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/35700
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-by: Bala.FA <barumuga@redhat.com>
Reviewed-by: Petr Horáček <phoracek@redhat.com>