iscsi: Fix two regular expression patterns

Signed-off-by: Yanbing Du <ydu@redhat.com>
virttest.virsh: Add pool_create and vol_create_from APIs

Signed-off-by: Yanbing Du <ydu@redhat.com>
libvirt: Add new virsh_vol_create_from test

Test virsh vol-create-from command to cover the following matrix:

pool = [source, destination]
pool_type = [dir, disk, fs, logical, netfs, iscsi, scsi]
volume_format = [raw, qcow2, qed]

Note, both 'iscsi' and 'scsi' type pools don't support create volume
using virsh, so which can't be destination pools. And for disk pool,
it can't create volumes with specified format.

Signed-off-by: Yanbing Du <ydu@redhat.com>