virttest.virsh: Add domiflist function

Signed-off-by: Satheesh Rajendran <sathnaga@linux.vnet.ibm.com>
virsh_cmd: Add virsh domiflist test case

Step 1: Get the virsh domiflist value.
Step 2: Check for interface in xml file.
Step 3: Check for type in xml file.
Step 4: Check for model inside the guest and xml file.
Step 5: Check for mac id inside the guest and xml file.

Signed-off-by: Satheesh Rajendran <sathnaga@linux.vnet.ibm.com>