Server default bossThreadsCount is inconsistent

[kvosper]

The problem

If a Server is created with no bossThreadsCount, it will use half of available processors. If a Server is created without the relevant config bloc, it will use 1 thread. If a Server is created with bossThreadsCount=0, it will use the Netty default.

It should not have different defaults in different situations.

Acceptance criteria

• The same default is applied in all situations (half of available processors unless our design changes)