HBASE-12312 Another couple of createTable race conditions

Signed-off-by: stack <stack@apache.org>
Implement Preemptive Fast Fail

Summary: This diff ports the Preemptive Fast Fail feature to OSS. In multi threaded clients, we use a feature developed on 0.89-fb branch called Preemptive Fast Fail. This allows the client threads which would potentially fail, fail fast. The idea behind this feature is that we allow, among the hundreds of client threads, one thread to try and establish connection with the regionserver and if that succeeds, we mark it as a live node again. Meanwhile, other threads which are trying to establish connection to the same server would ideally go into the timeouts which is effectively unfruitful. We can in those cases return appropriate exceptions to those clients instead of letting them retry.

Test Plan: Unit tests

Differential Revision: https://reviews.facebook.net/D24177

Signed-off-by: stack <stack@apache.org>
Add more notes on why 0.96 -> 1.0 rolling upgrade not possible
Add note to upgrade section on HBASE-12068; i.e. things to do if you have custom filters