virt-libvirt: Modify virsh dump test and add some testcases

1. Instead of thread, use os.fork to create a new process,
   because we cannot get any exception in main process from
   another thread.
2. Add "try...finally" part at the end, because when test failed,
   config file won't be recovered.
3. Add 3 test cases for paused VM test.
4. Fix too many 'if' problem

Signed-off-by: Li Yang <liyang.fnst@cn.fujitsu.com>
virt-libvirt: Don't be ambiguous about string case

Sometimes file command retuns upper-case results and it's
possible someone could configure a format w/ mixed case.
Instead, be clear and always compare as lower-case.

Signed-off-by: Chris Evich <cevich@redhat.com>