svirt_start_destroy: Add more test cases

2014-08-26 Update:
Moved the attach pool vol disk cases to new PR 302

svirt_start_destroy: Add test cases with security_driver as none
svirt_start_destroy: Add bug number to label restore FAIL cases
svirt_start_destroy: Update seclabel functions
Update set_seclabel use list in svirt test cases
svirt_start_destroy: Add cases for multiple seclabels
svirt_start_destroy: Add cases for security_default_confined as 0
svirt_start_destroy: Add negative cases for security_require_confined as 1
Checked: 
```
# vim virttest/libvirt_vm.py +1584
```

it could be shutdown first if shutdown_command in params, I'll update it.