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 #356 from PandaWei/virt-cmd

Add try/except for os_dep.command failure
Merge pull request #333 from waynesun09/acl_interface

virsh_iface: Add acl test cases for virInterfacePtr group apis
virt_xml_validate: Add more cases for other schemas

new supported schemas including below:
    domainsnapshot, network, storagepool, storagevol,
    nodedev, capability, nwfilter, secret, interface