Libvirt: Minor fix for libvirt test.

  utils_selinux_unittest: replace assertIn with assertTrue.
  Fix virsh.start to return CmdResult object
  Fix dummyvirsh.define() to return CmdResultObject.
  Fix the context_pattern in get_context_from_str method.

 virttest/libvirt_vm.py              |    3 ++-
 virttest/libvirt_xml/nodedev_xml.py |    3 ++-
 virttest/libvirt_xml_unittest.py    |    7 +++++++
 virttest/utils_selinux.py           |    2 +-
 virttest/utils_selinux_unittest.py  |    4 ++--
 virttest/virsh.py                   |   12 ++----------
 6 files changed, 16 insertions(+), 15 deletions(-)