Add wrapper Python script to replace run-playbook

The wrapper lets us be more user-friendly, with a nicer syntax and
better checks and error messages. It might eventually evolve to
include other functionality such as admin user management etc.

float

+#!/usr/bin/env python
+
+from __future__ import print_function
+
+import argparse
+import os
+import subprocess
+import sys
+
+
+# Find the root ai3/float source directory.
+srcdir = os.path.dirname(__file__)
+
+
+def support_ansible_vault_gpg_passphrase():
+    """Support GPG-encrypted Ansible Vault passphrases.
+
+    We do this by rewriting the ANSIBLE_VAULT_PASSWORD_FILE
+    environment variable and pointing it at a wrapper script.
+
+    The function does not return anything but as a side effect it will
+    modify os.environ (so that the subprocess modulee will pick up the
+    changes).
+
+    """
+    pwfile = os.getenv('ANSIBLE_VAULT_PASSWORD_FILE')
+    if not pwfile:
+        raise Exception(
+            'The environment variable ANSIBLE_VAULT_PASSWORD_FILE is not '
+            'defined. You should point it at the file containing your '
+            'Ansible Vault passphrase (possibly encrypted with GPG).')
+    if not os.path.exists(pwfile):
+        raise Exception(
+            'The ANSIBLE_VAULT_PASSWORD_FILE (%s) does not exist.' % (
+                pwfile,))
+
+    # Be friendly to the user and resolve tilde (~ and ~user) paths,
+    # which the shell would not do otherwise in environment variables.
+    # Then ensure it is an absolute path.
+    pwfile = os.path.abspath(os.path.expanduser(pwfile))
+
+    # If the file has a .gpg extension, wrap it with our decoding
+    # script: Ansible will execute the script due to its +x
+    # permissions, which in turn will use gpg to decrypt the
+    # passphrase (using another environment variable to find the
+    # original file).
+    if pwfile.endswith('.gpg'):
+        os.environ['FLOAT_VAULT_PASSWORD_FILE'] = pwfile
+        pwfile = os.path.join(scrdir, 'scripts', 'get-vault-password')
+
+    os.environ['ANSIBLE_VAULT_PASSWORD_FILE'] = pwfile
+
+
+def command_run(config, playbooks):
+    for arg in playbooks:
+        if not os.path.exists(arg):
+            # See if we have a stock playbook with that name.
+            if not arg.endswith('.yml'):
+                arg += '.yml'
+            pbk = os.path.join(srcdir, 'playbooks', arg)
+            if os.path.exists(pbk):
+                arg = pbk
+
+        print('Running playbook %s...' % (arg,))
+
+        os.environ['LC_ALL'] = 'C'
+        support_ansible_vault_gpg_passphrase()
+        subprocess.check_call(
+            [os.getenv('ANSIBLE_PLAYBOOK', 'ansible-playbook'),
+             '-i', config, arg])
+
+
+def command_init_credentials(config):
+    command_run(config, ['init-credentials.yml'])
+
+
+def main():
+    parser = argparse.ArgumentParser(
+        description='Container-based cluster management CLI.')
+    parser.add_argument(
+        '--config', metavar='file', default='config.yml',
+        help='Path to the configuration file')
+
+    subparsers = parser.add_subparsers(dest='subparser')
+
+    help_parser = subparsers.add_parser(
+        'help', help='print help')
+
+    run_parser = subparsers.add_parser(
+        'run',
+        help='run Ansible playbooks',
+        description='Run Ansible playbooks.')
+    run_parser.add_argument(
+        'playbooks', metavar='playbook', nargs='*',
+        default=['site.yml'], help='Playbooks to run')
+
+    init_credentials_parser = subparsers.add_parser(
+        'init-credentials',
+        help='initialize credentials',
+        description='Initialize credentials.')
+
+    args = parser.parse_args()
+    kwargs = vars(parser.parse_args())
+    cmd = kwargs.pop('subparser')
+
+    if cmd == 'help' or not cmd:
+        parser.print_help()
+        return
+
+    if not os.path.exists(args.config):
+        raise Exception(
+            'The configuration file %s does not exist!' % (args.config,))
+
+    handler = 'command_' + cmd.replace('-', '_')
+    globals()[handler](**kwargs)
+
+
+if __name__ == '__main__':
+    try:
+        main()
+    except Exception as e:
+        print("ERROR: %s" % (str(e),), file=sys.stderr)
+        sys.exit(1)