OSHMEM: better error messages when failing

Provide users with right fail reason.

fixes #4433
osc/rdma: fix bug in the active message code that could cause erroneous
results

The code to handle completion messages did not correctly increment the
number of expected messages. This could cause wait to return before all
incoming messages are complete.

I also added a check to ensure that start returns an error if we are in
a passive access epoch.

cmr=v1.8:reviewer=jsquyres
osc: fix datatype related issues in the one-sided code

This commit fixes two issues:

 - osc/rdma: The target side of an accumulate was using the target datatype
   in the receive to the packed buffer. This was conflicting with the way
   the reduction is done into the target buffer. Changed the receive to use
   the primitive datatype.

 - osc/base: The copy table was completely wrong. Fixed the table to match
   the underlying datatypes (which are opal not ompi datatypes).

 - osc/base: There is a problem using the optimized description. Fall back
   on using the non-optimized description until we can understand what is
   going wrong.

cmr=v1.8:reviewer=jsquyres