libvirt-tests: Fix some emulatorpin errors

* Backup vm's xml for restoration. or the vm xml will change for
  set_emulatorpin cases.

* Move the test process into a try/finally block to ensure environment
  is cleaned up even if exception raised.

* Fix typo in cfg file causing duplicated test name: s/config/live

Signed-off-by: Hao Liu <hliu@redhat.com>