Remove unrecheable code

os.execlp() does not return if successful. From the documentation[1]:

"These functions all execute a new program, replacing the current
process; they do not return".

[1] https://docs.python.org/3/library/os.html#os.execlp

Change-Id: I03776591f225348ffda5204eddbce24b1c465753
Signed-off-by: Youngjun <yj.yoo@okestro.com>

glance/cmd/control.py

@@ -173,7 +173,6 @@ def do_start(verb, pid_file, server, args):
                 msg = (_('unable to launch %(serv)s. Got error: %(e)s') %
                        {'serv': server, 'e': e})
                 sys.exit(msg)
-            sys.exit(0)
         else:
             write_pid_file(pid_file, pid)
             await_child(pid, await_time)