Removed stderr pipe to stdout on pg_ctl process (#896)

Inheriting stderr from the main Patroni process allows all Postgres logs to be seen along with all patroni logs. This is very useful in a container environment as Patroni and Postgres logs may be consumed using standard tools (docker logs, kubectl, etc).

In addition to that, this change fixes a bug with Patroni not being able to catch postmaster pid when postgres writing some warnings into stderr

patroni/postmaster.py

@@ -157,7 +157,7 @@ def start(pgcommand, data_dir, conf, options):
         cmdline = [pgcommand, '-D', data_dir, '--config-file={}'.format(conf)] + options
         logger.debug("Starting postgres: %s", " ".join(cmdline))
         proc = call_self(['pg_ctl_start'] + cmdline, close_fds=(os.name != 'nt'),
-                         stdout=subprocess.PIPE, stderr=subprocess.STDOUT, env=env)
+                         stdout=subprocess.PIPE, env=env)
         pid = int(proc.stdout.readline().strip())
         proc.wait()
         logger.info('postmaster pid=%s', pid)