btl/openib: Move free list memory allocation to add_procs

Per RFC which expired two weeks ago:

We are planning to make a change to Open MPI to always set up the btls. This
means the btl init will be called even if add_procs is never called for that
btl. In the openib btl free lists fragments are currently allocated in btl_init.
To avoid wasting that memory this commit moves that final device setup to
the add_procs function. This included allocating free lists, and starting the
async event thread.

At this time this change is safe since we have a barrier after add_procs in
MPI_Init. If this changes we will need to re-think some of the initialization
since we might have the possibility of a connection request before add_procs
is called.

Tested with Mellanox ConnectX2 and QLogic HCAs.

Commit also cleans up tabs in btl_openib_async.c.

cmr=v1.7.5:reviewer=miked
btl/vader: add support for traditional shared memory.

This commit adds support for placing the send memory segment in a
traditional shared memory segment when XPMEM is not available. The
current default is to reserve 4MB for shared memory on each process.
The latest benchmarks show vader performing better than sm on both
Intel and AMD CPUs.

For large messages vader will now use CMA if it is available (and
XPMEM is not).

cmr=v1.7.5:reviewer=jsquyres