Run mlock_report under python3

psutil is only installed under python3 for the 3.5 gate jobs.  Call
mlock_report.py with $PYTHON so we support both environments.

Updates to mlock_report.py for python3 compatability

Change-Id: If7926ce6a2996b766c49b010a7f6640ae624f860
diff --git a/tools/mlock_report.py b/tools/mlock_report.py
index 1d23af9..2169cc2 100755
--- a/tools/mlock_report.py
+++ b/tools/mlock_report.py
@@ -8,14 +8,15 @@
 import psutil
 
 
-SUMMARY_REGEX = re.compile(r".*\s+(?P<locked>[\d]+)\s+KB")
+SUMMARY_REGEX = re.compile(b".*\s+(?P<locked>[\d]+)\s+KB")
 
 
 def main():
     try:
-        print _get_report()
+        print(_get_report())
     except Exception as e:
-        print "Failure listing processes locking memory: %s" % str(e)
+        print("Failure listing processes locking memory: %s" % str(e))
+        raise
 
 
 def _get_report():