Fix multi-namespace SDL event subscribe

Fix multi-namespace SDL event subscribe

SDL event channel internal format was wrongly showed to application
when the same application instance was subscribing to receive SDL
events from multiple namespaces. In that case subscribes were all
registered to the first namespace in SDL and hence when an event in a
channel belonging to another namespace was triggered, namespace internal
format '{other-namespace},' was showed in front of channel name. With
this commit change namespace lookup from channel name to search from
left to right the first comma ',' character. String after comma is
a channel name what should be showed to an application and all before
the comma ',' character can be silently parsed away in SDL.

Issue-Id: RIC-885

Signed-off-by: Timo Tietavainen <timo.tietavainen@nokia.com>
Change-Id: I90b94862670e1e529381112e385b65250e7cb275