Converse: Add API to initialize converse message header fields
void CmiInitMsgHeader(void *msg, int size) is the newly added method
that allows a user to set the converse message fields to desired
defaults. Currently, only zcMsgType is being set to CMK_REG_NO_ZC_MSG
inside CmiInitMsgHeader. This initialization is performed internally
for all allocations made using CmiAlloc and CmiRdmaAlloc. It needs
to be explicitly called for Charm++/Converse message allocations made
without these calls.
Change-Id: I843dbe5264cfbf6efc755ef781f36974ef533da0