[FIX] #734 Whiteboard can stall forever in the network layer 

The inviter's Whiteboard waits only 30 sec for a response from the
invitee.

Pair-programmed-with: Franz Zieris

Change-Id: I2651743ddacfe59c3cd228326c4dcd0af735f5ff
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1505
Tested-by: Jenkins CI
Reviewed-by: Damla Durmaz <ddurmaz88@gmail.com>
Reviewed-by: Bernd Bieber <brotlee@zedat.fu-berlin.de>
Reviewed-by: Franz Zieris <zieris@inf.fu-berlin.de>