ALLJOYN-2514: Key blob is always little-endian now.

Previously a big-endian host would send the key blob in big-endian
order via ExchangeGroupKeys.  This would then be interpreted as a
corrupt key blob by little-endian host.

Change-Id: Ia8c135ca302606f63a499c1d5b6d28f8814168a9
Fix darwin build.

Change-Id: I9a48e965f6d1197c915b3c67ae7fb3645d4e2e15