snapshot_disk: Add snapshot_delete cases without '--metadata' option

External disk only snapshot is not supported with delete yet, but internal
snapshot delete is supported. Update test case and cfg to support testing
this.

Add filter 'delete_test' to cover 6 new delete cases, put exist cases
under 'no_delete'.

The original cases total is 27, now with 6 new delete cases, total will
be 33.

Fixed few lines with column length exceeds 80.

Signed-off-by: Wayne Sun <gsun@redhat.com>
snapshot_disk: Fix error cases for internal diskonly and external revert

Internal disk only snapshot will fail since commit d2e668e in libvirt
1.2.5, and external revert will fail since d410e6f in libvirt 1.2.3.

Following bugs is tracking for this:
https://bugzilla.redhat.com/show_bug.cgi?id=1071264
https://bugzilla.redhat.com/show_bug.cgi?id=1083345

Signed-off-by: John Ferlan <jferlan@redhat.com>
Signed-off-by: Wayne Sun <gsun@redhat.com>
Merge pull request #182 from waynesun09/snapshot_delete

snapshot_disk: Add snapshot_delete cases without '--metadata' option