puppet: Pass zulip scripts path as a FACTER to puppet.

This makes it possible for the Puppet codebase to access the path to
the relevant /home/zulip/deployments type directory that puppet was
run from, which in turn makes it possible to safely call scripts from
here.

Based on work by Rein Zustand.

scripts/zulip-puppet-apply

@@ -8,6 +8,7 @@ import re
 from lib.zulip_tools import parse_lsb_release, assert_running_as_root
 
 assert_running_as_root()
+BASE_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
 
 force = False
 extra_args = sys.argv[1:]
@@ -34,12 +35,17 @@ for pclass in re.split(r'\s*,\s*', config.get('machine', 'puppet_classes')):
     puppet_config += "include %s\n" % (pclass,)
 
 # We use the puppet configuration from the same Zulip checkout as this script
-puppet_module_path = os.path.join(os.path.dirname(os.path.dirname(os.path.abspath(__file__))), "puppet")
+scripts_path = os.path.join(BASE_DIR, "scripts")
+puppet_module_path = os.path.join(BASE_DIR, "puppet")
 puppet_cmd = ["puppet", "apply", "--modulepath", puppet_module_path, "-e", puppet_config]
 puppet_cmd += extra_args
 
+# Set the scripts path to be a factor so it can be used by puppet code
+puppet_env = os.environ.copy()
+puppet_env["FACTER_zulip_scripts_path"] = scripts_path
+
 if not force:
-    subprocess.check_call(puppet_cmd + ['--noop', '--show_diff'])
+    subprocess.check_call(puppet_cmd + ['--noop', '--show_diff'], env=puppet_env)
 
     do_apply = None
     while do_apply != 'y':
@@ -49,7 +55,7 @@ if not force:
         if do_apply == '' or do_apply == 'n':
             sys.exit(0)
 
-ret = subprocess.call(puppet_cmd + ['--detailed-exitcodes'])
+ret = subprocess.call(puppet_cmd + ['--detailed-exitcodes'], env=puppet_env)
 # ret = 0 => no changes, no errors
 # ret = 2 => changes, no errors
 # ret = 4 => no changes, yes errors