Rebase: Add virsh testcase virsh_blockresize

  domain/virsh_blockresize.py
  domain/virsh_blockresize.cfg

Signed-off-by: Guannan Ren <gren@redhat.com>

Rebase on https://github.com/autotest/tp-libvirt/pull/37

changes:
Parsing cases of virsh.blockresize wrong because qcow2 and raw are conflict with exist 'variant'.
So renaming them to qcow2_type and raw_type.(not clear about the root reason)