timedated: flip internal status after executing operation

timedated would set the internal status before calling out to systemd to do
the actual change. When the operation was refused because of a SELinux denial,
the state kept in timedated would get out of sync, and the second call from
timedatectl would appear to succeed.

https://bugzilla.redhat.com/show_bug.cgi?id=1014315

(cherry picked from commit 192b98b8)
(cherry picked from commit fb14f86a)

[Amended to reverse the condition.]