use per-language dockerfiles
diff --git a/tools/run_tests/run_tests.py b/tools/run_tests/run_tests.py
index 6dfdc70..f405866 100755
--- a/tools/run_tests/run_tests.py
+++ b/tools/run_tests/run_tests.py
@@ -186,7 +186,7 @@
     return True
 
   def dockerfile_dir(self, config, arch):
-    return None
+    return 'tools/dockerfile/test/cxx_jessie_%s' % _docker_arch_suffix(arch)
 
   def __str__(self):
     return self.make_target
@@ -225,7 +225,7 @@
     return False
 
   def dockerfile_dir(self, config, arch):
-    return None
+    return 'tools/dockerfile/test/node_jessie_%s' % _docker_arch_suffix(arch)
 
   def __str__(self):
     return 'node'
@@ -259,7 +259,7 @@
     return False
 
   def dockerfile_dir(self, config, arch):
-    return None
+    return 'tools/dockerfile/test/php_jessie_%s' % _docker_arch_suffix(arch)
 
   def __str__(self):
     return 'php'
@@ -315,7 +315,7 @@
     return False
 
   def dockerfile_dir(self, config, arch):
-    return None
+    return 'tools/dockerfile/test/python_jessie_%s' % _docker_arch_suffix(arch)
 
   def __str__(self):
     return 'python'
@@ -349,7 +349,7 @@
     return False
 
   def dockerfile_dir(self, config, arch):
-    return None
+    return 'tools/dockerfile/test/ruby_jessie_%s' % _docker_arch_suffix(arch)
 
   def __str__(self):
     return 'ruby'
@@ -434,7 +434,7 @@
     return False
 
   def dockerfile_dir(self, config, arch):
-    return None
+    return 'tools/dockerfile/test/csharp_jessie_%s' % _docker_arch_suffix(arch)
 
   def __str__(self):
     return 'csharp'
@@ -506,7 +506,7 @@
     return False
 
   def dockerfile_dir(self, config, arch):
-    return 'tools/dockerfile/grpc_sanity'
+    return 'tools/dockerfile/test/sanity'
 
   def __str__(self):
     return 'sanity'
@@ -630,19 +630,24 @@
     sys.exit(1)
 
 
+def _docker_arch_suffix(arch):
+  """Returns suffix to dockerfile dir to use."""
+  if arch == 'default' or arch == 'x64':
+    return 'x64'
+  elif arch == 'x86':
+    return 'x86'
+  else:
+    print 'Architecture %s not supported with current settings.' % arch
+    sys.exit(1)
+
+
 def _get_dockerfile_dir(language, cfg, arch):
   """Returns dockerfile to use"""
   custom = language.dockerfile_dir(cfg, arch)
   if custom:
     return custom
   else:
-    if arch == 'default' or arch == 'x64':
-      return 'tools/dockerfile/grpc_tests_multilang_x64'
-    elif arch == 'x86':
-      return 'tools/dockerfile/grpc_tests_multilang_x86'
-    else:
-      print 'Architecture %s not supported with current settings.' % arch
-      sys.exit(1)
+    return 'tools/dockerfile/grpc_tests_multilang_%s' % _docker_arch_suffix(arch)
 
 def runs_per_test_type(arg_str):
     """Auxilary function to parse the "runs_per_test" flag.