Remove state_dir requirement from merger

The merger process does not use the state_dir, remove the check
that it exists.  It was already undocumented, so this now matches
the documentation.

Change-Id: Ie8cbe75ce4dff774b3f5b3bdaaf324fd9ba6698f

tests/base.py

@@ -1940,7 +1940,6 @@ class ZuulTestCase(BaseTestCase):
                             self.config.get('scheduler', 'tenant_config')))
         self.config.set('scheduler', 'state_dir', self.state_root)
         self.config.set('merger', 'git_dir', self.merger_src_root)
-        self.config.set('merger', 'state_dir', self.merger_state_root)
         self.config.set('executor', 'git_dir', self.executor_src_root)
         self.config.set('executor', 'private_key_file', self.private_key_file)
         self.config.set('executor', 'state_dir', self.executor_state_root)

zuul/cmd/merger.py

@@ -22,7 +22,6 @@ import extras
 # instead it depends on lockfile-0.9.1 which uses pidfile.
 pid_file_module = extras.try_imports(['daemon.pidlockfile', 'daemon.pidfile'])
 
-import os
 import sys
 import signal
 
@@ -80,17 +79,6 @@ def main():
     server.read_config()
     server.configure_connections(source_only=True)
 
-    state_dir = get_default(server.config, 'merger', 'state_dir',
-                            '/var/lib/zuul', expand_user=True)
-    test_fn = os.path.join(state_dir, 'test')
-    try:
-        f = open(test_fn, 'w')
-        f.close()
-        os.unlink(test_fn)
-    except Exception:
-        print("\nUnable to write to state directory: %s\n" % state_dir)
-        raise
-
     pid_fn = get_default(server.config, 'merger', 'pidfile',
                          '/var/run/zuul-merger/zuul-merger.pid',
                          expand_user=True)