dompmsuspend: Add VM S3/S4 enable/disable test

1) Test enable and disable VM's S3/S4 capabilities in pm tag.
2) Update test case to check standard error message.
3) Activate a swap partition if the VM don't have one when testing
   S4.
4) Remove unneeded check of pm-utils installation.

Signed-off-by: Hao Liu <hliu@redhat.com>
Merge pull request #254 from Hao-Liu/add_pm_test

dompmsuspend: Add VM S3/S4 enable/disable test