Don't enforce foreground with -d switch

We have a separate switch in place to enforce running in foreground so
it's time to decouple debug logging from running in foreground.

Change-Id: I5ad1138b0054786686a8b22aece1a473be88eee0

releasenotes/notes/foreground-15824166b5fb7e80.yaml

@@ -0,0 +1,5 @@
+---
+upgrade:
+  - |
+    The -d switch doesn't enforce foreground anymore. It only enables debug
+    logging. To start zuul in foreground please add the -f switch instead.

zuul/cmd/__init__.py

@@ -121,10 +121,7 @@ class ZuulApp(object):
         parser = self.createParser()
         self.args = parser.parse_args(args)
 
-        # The arguments debug and foreground both lead to nodaemon mode so
-        # set nodaemon if one of them is set.
-        if ((hasattr(self.args, 'debug') and self.args.debug) or
-                (hasattr(self.args, 'foreground') and self.args.foreground)):
+        if hasattr(self.args, 'foreground') and self.args.foreground:
             self.args.nodaemon = True
         else:
             self.args.nodaemon = False
@@ -174,13 +171,9 @@ class ZuulDaemonApp(ZuulApp, metaclass=abc.ABCMeta):
     def createParser(self):
         parser = super(ZuulDaemonApp, self).createParser()
         parser.add_argument('-d', dest='debug', action='store_true',
-                            help='run in foreground with debug log. Note '
-                                 'that in future this will be changed to only '
-                                 'request debug logging. If you want to keep '
-                                 'running the process in the foreground '
-                                 'migrate/add the -f switch.')
+                            help='enable debug log')
         parser.add_argument('-f', dest='foreground', action='store_true',
-                            help='run in foreground with info log')
+                            help='run in foreground')
         return parser
 
     def getPidFile(self):