clean-npm-cache: Expand clean-npm-cache.

Expands `clean-npm-cache` so that it can be used in production
environment as well. Also moves it to `scripts/` from `tools/`.

scripts/clean-npm-cache

@@ -0,0 +1,67 @@
+#!/usr/bin/env python3
+import argparse
+import os
+import subprocess
+import sys
+
+if False:
+    from typing import Set, Text
+
+ZULIP_PATH = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+sys.path.append(ZULIP_PATH)
+from scripts.lib.node_cache import generate_sha1sum_node_modules
+from scripts.lib.zulip_tools import GENERIC_CACHE_SCRIPT_PARSER, \
+    get_caches_to_be_purged, get_environment, get_recent_deployments, \
+    purge_unused_caches
+
+ENV = get_environment()
+NODE_MODULES_CACHE_PATH = "/srv/zulip-npm-cache"
+if ENV == "travis":
+    NODE_MODULES_CACHE_PATH = os.path.join(os.environ["HOME"], "zulip-npm-cache")
+    try:
+        subprocess.check_output(["/srv/zulip-yarn/bin/yarn", '--version'])
+    except OSError:
+        print('yarn not found. Most probably we are running static-analysis and '
+              'hence yarn is not installed. Exiting without cleaning npm cache.')
+        sys.exit(0)
+
+def parse_args():
+    # type: () -> argparse.Namespace
+    parser = argparse.ArgumentParser(description="This script cleans unused zulip npm caches.",
+                                     parents=[GENERIC_CACHE_SCRIPT_PARSER, ])
+    args = parser.parse_args()
+    return args
+
+def get_caches_in_use(threshold_days):
+    # type: (int) -> Set[Text]
+    setups_to_check = set([ZULIP_PATH, ])
+    caches_in_use = set()
+
+    if ENV == "prod":
+        setups_to_check |= get_recent_deployments(threshold_days)
+    if ENV == "dev":
+        # In dev always include the currently active cache in order
+        # not to break current installation in case dependencies
+        # are updated with bumping the provision version.
+        CURRENT_CACHE = os.path.dirname(os.path.realpath(os.path.join(ZULIP_PATH, "node_modules")))
+        caches_in_use.add(CURRENT_CACHE)
+
+    for setup_dir in setups_to_check:
+        PACKAGES_FILE = os.path.join(setup_dir, "package.json")
+        if os.path.exists(PACKAGES_FILE):
+            # If 'package.json' file doesn't exist then no node_modules
+            # cache is associated with this setup.
+            sha1sum = generate_sha1sum_node_modules(setup_dir=setup_dir)
+            caches_in_use.add(os.path.join(NODE_MODULES_CACHE_PATH, sha1sum))
+
+    return caches_in_use
+
+def main():
+    # type: () -> None
+    args = parse_args()
+    caches_in_use = get_caches_in_use(args.threshold_days)
+    purge_unused_caches(
+        NODE_MODULES_CACHE_PATH, caches_in_use, args.threshold_days, args.dry_run, "node modules")
+
+if __name__ == "__main__":
+    main()