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
I think it could be more reliable to move all setters like `set_context_of_file`, `os.chown`, `utils_selinux.set_status` to `try ... finally ...` block, leaving only getters for backing up outside. This tends to eliminate possibilities of destroying environment when any of there setter happens to fail in extreme condition.