virsh_iface: Add acl test cases for virInterfacePtr group apis

Add acl test cases for 'write', 'save', 'start', 'stop' and 'delete'
in virInterfacePtr group.

Signed-off-by: Wayne Sun <gsun@redhat.com>
iface: Add acl case for iface list and dumpxml command

iface list and dumpxml command works by default with no permission
restriction, the commit add test for grant none to test both
command works as expected.

Signed-off-by: Wayne Sun <gsun@redhat.com>
Merge pull request #333 from waynesun09/acl_interface

virsh_iface: Add acl test cases for virInterfacePtr group apis
virsh_iface_bridge: add checkpoints for iface-bridge test

add two checkpoints for the test of iface-bridge command
1) The new bridge's IP should keep the same as original interface' IP.
2) If '--no-stp' option isn't specified, the STP should be enabled.