The test xenapi/vm_rrd.xml file was opened in test_xenapi.py relative to
the current working directory. This forced you to run unittests out of
the nova/tests directory. Open the xenapi/vm_rrd.xml relative to the
test_xenapi.py file so that the current working directory does not
matter.
Part of blueprint grizzly-testtools
Change-Id: I2b8720ea418e10e9748adaa599513794202351e6