Unify initial waiting of debug services

The debug services generally behave in one of two ways when initializing:
Either they block the initializing thread until some configuration is
passed over the network or they just go on. By introducing a generalized
configurable debug service the various ways of waiting on initialization
are cleaned up. The API defined for it also allows for engine-specific
initialization.

Change-Id: Id5685ef17d2a7eb1222629f7caa5ec53076d47b2
Reviewed-by: Kai Koehne <kai.koehne@digia.com>