Collect all env vars in one, easy-to-find place (#1149)

* Collect all env vars in one, easy-to-find place

Past state:
* Default environement variables were stored in both client/package.json
and client/__tests__/e2e/config.js
* Constants that should have been linked--like the cellxgene server port
during testing--were repeated.

With this commit:
* All environment variables are parameterized
* All environment variables are packaged in default env files

* Move npm scripts to client Makefile

* Respond to feedback from @seve and @bkmartinjr

scripts/await_port

@@ -0,0 +1,58 @@
+#!/usr/bin/env python3
+import argparse
+import errno
+import socket
+import sys
+import time
+
+# await_port
+#
+# Functionality:
+# 1. Wait for a process to be listening on a port - await_port will poll the address with a bind request and close it
+#    until another process takes the address.
+# 2. Wait for a port to be free - await_port will poll the address with a bind request and close it until the port is
+#    free.
+
+parser = argparse.ArgumentParser(description='Wait for a port either to be bound to or to be free.')
+parser.add_argument('port', type=int, help='port to wait for')
+parser.add_argument('--sleep-increment', type=int, default=2.0, help='sleep duration in between checks of the port')
+parser.add_argument('--timeout', type=int, default=20.0, help='How long should we wait before timing out?')
+parser.add_argument('--await-free', default=False, action='store_true',
+                    help='Wait for the port to be active or free?')
+
+args = parser.parse_args()
+
+start = time.time()
+
+port_in_use = None
+
+desired_state = 'free' if args.await_free else 'in use'
+
+
+def condition_reached(port_in_use):
+    return not port_in_use if args.await_free else port_in_use
+
+
+while True:
+    # halt if we've reached the timeout
+    elapsed = time.time() - start
+    if elapsed > args.timeout:
+        print(f"Timed out while waiting for port {args.port}")
+        sys.exit(1)
+
+    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
+        try:
+            s.bind(('localhost', args.port))
+            port_in_use = False
+        except socket.error as e:
+            if e.errno != errno.EADDRINUSE:
+                raise e
+            port_in_use = True
+
+    if condition_reached(port_in_use):
+        break
+
+    print(f"Waiting for port {args.port} to be {desired_state}... sleeping for {args.sleep_increment} seconds.")
+    time.sleep(args.sleep_increment)
+
+print(f"Port {args.port} is {desired_state}!")

scripts/start_server_and_test

@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+set -e
+
+# start_server_and_test
+# Replicates the basic functionality of the start-server-and-test npm package
+# https://www.npmjs.com/package/start-server-and-test
+
+if [[ $# -ne 3 ]]; then
+  echo "Usage: start_server_and_test \'[start server script]\' [port] \'[test script]\'"
+  exit 1
+fi
+
+START_SERVER_SCRIPT="$1"
+PORT="$2"
+TEST_SCRIPT="$3"
+
+eval "$START_SERVER_SCRIPT &"
+SERVER_PID=$!
+
+function finish {
+  kill $SERVER_PID || true
+}
+
+trap finish EXIT
+
+await_port "$PORT"
+
+eval "$TEST_SCRIPT"