dal: Added a mixed storage pool to fixtures.xml

Added a mixed storage pool to fixtures.xml file to allow dao tests to test
cases of mixed storage pools also

Change-Id: I285c420902ce8d28cb7e8bfcc2ad3a11c225c0fb
Bug-Url: https://bugzilla.redhat.com/1085395
Signed-off-by: Tal Nisan <tnisan@redhat.com>