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

tools/memory_tracker.sh

@@ -14,6 +14,8 @@
 
 set -o errexit
 
+PYTHON=${PYTHON:-python}
+
 # time to sleep between checks
 SLEEP_TIME=20
 
@@ -86,7 +88,7 @@ function tracker {
             # list processes that lock memory from swap
             if [[ $unevictable -ne $unevictable_point ]]; then
                 unevictable_point=$unevictable
-                ./tools/mlock_report.py
+                ${PYTHON} ./tools/mlock_report.py
             fi
 
             echo "]]]"

tools/mlock_report.py

@@ -8,14 +8,15 @@ import subprocess
 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():