Make testing toolchain python 3.x compliant

six is necessary for making these scripts cross compatible
between python 2.x and 3.x

Changes:
Add six to python_deps.include
Include python_deps.include to all Dockerfile templates in test directory
Include python_deps.include to all Dockerfile templates in stress_test directory
Include python_deps.include to all Dockerfile templates in interop_test directory
Replace print statements with print function calls (from futute..)
Replace .iteritems() with .items() wherever necessary
use six.moves to import BaseHTTPServer
Generate new dockerfiles using generate_projects.sh
diff --git a/tools/run_tests/task_runner.py b/tools/run_tests/task_runner.py
index b42aa17..2e3fa44 100755
--- a/tools/run_tests/task_runner.py
+++ b/tools/run_tests/task_runner.py
@@ -30,6 +30,8 @@
 
 """Runs selected gRPC test/build tasks."""
 
+from __future__ import print_function
+
 import argparse
 import atexit
 import jobset
@@ -111,7 +113,7 @@
 for target in targets:
   build_jobs.append(target.build_jobspec())
 if not build_jobs:
-  print 'Nothing to build.'
+  print('Nothing to build.')
   sys.exit(1)
 
 jobset.message('START', 'Building targets.', do_newline=True)