Consolidate the logic of sending update messages on FrameworkInfo changes.

Currently the logic of sending FRAMEWORK_UPDATED event and UpdateFrameworkMessage is scattered throughout different code paths on which framework re-subscription occurs.

On some of the paths the UpdateFrameworkMessage message is not being sent to slaves,  which looks like a bug:
https://github.com/apache/mesos/blob/6eeee96f98d5df02e937bee6f701b788bfb28de9/src/master/master.cpp#L3149

Moreover, the UPDATE_FRAMEWORK call (https://issues.apache.org/jira/browse/MESOS-7258) adds one more code path on which these messages are sent.

This logic is already very error-prone and makes it difficult to keep the side-effects of the UPDATE_FRAMEWORK call consistent with the framework re-subscription.

One of the possible approaches is to move this logic into the existing Master::updateFramework(Framework*, ...) method, which is called on all of these paths.
NOTE: there are at least two things which might require a special care with this approach:

• Information about framework state, reregistration time and so on in the the FRAMEWORK_UPDATED event.
• Ordering between relinking to the framework and sending UpdateFrameworkMessage.