Updating emulator script for non-legacy datastore emulator.

- Adding "--no-legacy" flag to "gcloud" CLI calls
- Updating instructions in CONTRIBUTING document to showcase
  the flag and the GCLOUD_DISABLE_GRPC env. var.
- Updating the datastore ready line for the server from
  the cloud-datastore-emulator (i.e. "--no-legacy") component,
  since it is different from the "gcd-emulator" component

CONTRIBUTING.rst

@@ -208,13 +208,14 @@ Running System Tests
   ``datastore`` emulator::
 
    $ tox -e datastore-emulator
+   $ GOOGLE_CLOUD_DISABLE_GRPC=true tox -e datastore-emulator
 
   This also requires that the ``gcloud`` command line tool is
   installed. If you'd like to run them directly (outside of a
   ``tox`` environment), first start the emulator and
   take note of the process ID::
 
-   $ gcloud beta emulators datastore start 2>&1 > log.txt &
+   $ gcloud beta emulators datastore start --no-legacy 2>&1 > log.txt &
    [1] 33333
 
   then determine the environment variables needed to interact with

system_tests/run_emulator.py

@@ -35,7 +35,10 @@
     'datastore': (GCD_DATASET, GCD_HOST),
     'pubsub': (PUBSUB_EMULATOR,)
 }
-_DS_READY_LINE = '[datastore] INFO: Dev App Server is now running\n'
+EXTRA = {
+    'datastore': ('--no-legacy',),
+}
+_DS_READY_LINE = '[datastore] Dev App Server is now running.\n'
 _PS_READY_LINE_PREFIX = '[pubsub] INFO: Server started, listening on '
 
 
@@ -62,7 +65,9 @@ def get_start_command(package):
     :rtype: tuple
     :returns: The arguments to be used, in a tuple.
     """
-    return 'gcloud', 'beta', 'emulators', package, 'start'
+    result = ('gcloud', 'beta', 'emulators', package, 'start')
+    extra = EXTRA.get(package, ())
+    return result + extra
 
 
 def get_env_init_command(package):
@@ -74,7 +79,9 @@ def get_env_init_command(package):
     :rtype: tuple
     :returns: The arguments to be used, in a tuple.
     """
-    return 'gcloud', 'beta', 'emulators', package, 'env-init'
+    result = ('gcloud', 'beta', 'emulators', package, 'env-init')
+    extra = EXTRA.get(package, ())
+    return result + extra
 
 
 def datastore_wait_ready(popen):

tox.ini

@@ -124,6 +124,8 @@ commands =
     python {toxinidir}/system_tests/run_emulator.py --package=datastore
 setenv =
     GOOGLE_CLOUD_NO_PRINT=true
+passenv =
+    GOOGLE_CLOUD_DISABLE_GRPC
 deps =
     {[testenv]deps}
     psutil