Set up pants.remote.ini for remoting Python unit tests (pantsbuild#7990)

Per pantsbuild#7649, we are working to remote unit tests in CI.

This implements step pantsbuild#2, which allows us to run unit tests locally (several, but not all tests). Here, we set up `pants.remote.ini` so that users only must point to it and provide the authentication token.

pants.remote.ini

@@ -0,0 +1,40 @@
+# For goals that you'd like to remote, first install the Google cloud CLI and then log in to an
+# an account authorized to run the Pants project (you may need to ask a Pants committer for
+# to authorize your account). Then, point to this config file and provide the oauth token like this:
+#
+#  $ ./pants --pants-config-files=pants.remote.ini
+#     --remote-oauth-bearer-token-path=<(gcloud auth application-default print-access-token | perl -p -e 'chomp if eof')
+#     --no-v1 --v2 test tests/python/pants_test/util:strutil
+#
+# Remoting does not work for every goal, so you should not permanently point to this ini file, e.g.
+# via an env var; only point to it when you want to remote a specific invocation.
+
+[DEFAULT]
+remote_execution: True
+remote_execution_server: remotebuildexecution.googleapis.com
+remote_store_server: remotebuildexecution.googleapis.com
+# This file might not exist on your machine. If this default fails, run `find /usr -name '*.pem'`
+# and override this value via the env var PANTS_REMOTE_CA_CERTS_PATH.
+remote_ca_certs_path: /usr/local/etc/openssl/cert.pem
+remote_instance_name: projects/pants-remoting-beta/instances/default_instance
+remote_execution_extra_platform_properties: [
+    # This allows network requests, e.g. to resolve dependencies with Pex.
+    "dockerNetwork=standard",
+    "container-image=docker://marketplace.gcr.io/google/rbe-ubuntu16-04@sha256:da0f21c71abce3bbb92c3a0c44c3737f007a82b60f8bd2930abc55fe64fc2729",
+  ]
+
+
+[python-setup]
+interpreter_search_paths: [
+     '<PEXRC>',
+     '<PATH>'
+     # TODO(#7735): We need to add this entry for remoting to be able to discover a valid
+     # interpreter, because <PATH> will refer to the host PATH and not the remote value. This value
+     # was found by inspecting the docker image for remoting.
+     "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/opt/python3.6/bin:/usr/local/go/bin",
+  ]
+
+
+[python-native-code]
+ld_flags: []
+cpp_flags: []