Add a thread for record vm register info in env_process

Add a thread for record vm register informations in env_process. 
Run a boot case seems OK:
18:24:10 WARNI| virt-tests-vm1 is not alive. Can not query the register status
18:24:11 INFO | PASS io-github-autotest-qemu.boot
18:24:11 INFO | 
 PASS (184.52 s)
18:24:11 INFO | Cleaning tmp files and VM processes...
18:24:11 WARNI| Creating new, empty env file
18:24:11 INFO | 
TOTAL TIME: 184.78 s (03:04)
18:24:11 INFO | Job total elapsed time: 184.78 s
TESTS PASSED: 1
TESTS FAILED: 0
SUCCESS RATE: 100.00 %