There are five options 'debug' 'labels' 'cluster-store' 'cluster-store-opts'
and 'cluster-advertise' that can be reconfigured, configure any of these
options should not affect other options which may have configured in flags.
But this is not true, for example, I start a daemon with -D to enable the
debugging, and after a while, I want reconfigure the 'label', so I add a file
'/etc/docker/daemon.json' with content '"labels":["test"]' and send SIGHUP to daemon
to reconfigure the daemon, it work, but the debugging of the daemon is also diabled.
I don't think this is a expeted behaviour.
This patch also have some minor refactor of reconfiguration of cluster-advertiser.
Enable user to reconfigure cluster-advertiser without cluster-store in config file
since cluster-store could also be already set in flag, and we only want to reconfigure
the cluster-advertiser.
Signed-off-by: Lei Jitang <leijitang@huawei.com>