Ensure that pipe_base testUtils is imported

The test file did not run standalone before but required
that the code had been imported via another file.

tests/test_commonMetrics.py

@@ -26,6 +26,7 @@
 import astropy.units as u
 
 import lsst.utils.tests
+import lsst.pipe.base.testUtils
 from lsst.pex.config import Config
 from lsst.pipe.base import Task
 from lsst.utils.timer import timeMethod