Cleanup bypass semantic in MasterCoprocessorHost

Lets decide on this one before we release 2.0.0.

A bunch of methods in MasterCoprocessorHost on the 'pre' step allow returning true which indicates the method invocation is not to proceed.

Not all 'pre' steps do this. Just some.

Seems a little arbitrary.

How we skip out if we are not proceed with the invocation is also a little arbitrary.

When a deleteColumn call is supposed to skip out, it returns a -1, a non-procId. If we are to skip a balance call, we log that CP said skip and then return false to indicate the balancer did not run (why?). Elsewhere we just exit silently. In createNamespace we used to exit silently but HBASE-14888 just changed it so we throw a BypassCoprocessorException instead...

Lets make them all work the same way.

(This issue comes of chat w/ Matteo)