JVMCBC-44 : let all ConfigRequest pass and adapt RequestHandlerTest

Motivation
-----------
All ConfigRequest should pass through the test for bucket presence in configuration.
Furthermore, after previous refactors the RequestHandlerTest's
test shouldRouteEventToNode would fail (config is empty in dummy).

Modifications
-------------
BootstrapMessage marker interface now on ConfigRequest instead of specific subtypes.
RequestHandlerTest modified to take into account the new need for a configuration that
can respond to hasBucket().

Result
------
All tests now pass.

Change-Id: I5e492ad0a64451dd7f6e654ea6f255c11f8490b7
Reviewed-on: http://review.couchbase.org/42236
Tested-by: Simon Baslé <simon@couchbase.com>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>