private data APIs are not allowed in Init() since the
private data collection configuration is not yet committed
on the channel.

This CR provide a better error message indicating that
pvtdata APIs are  not allowed in chaincode Init().

FAB-13050 #done

Change-Id: I6e6a8abdf1f35f56307be90d8b6b2830c8f35755
Signed-off-by: senthil <cendhu@gmail.com>