Fixes #3686: Add Cisco usNIC BTL to v1.7

---svn-pre-commit-ignore-below---

r28874 [[BR]]
Devices that do not support RC QP's are also intentionally skipped;
don't warn about skipping them.

r28879 [[BR]]
First commit of the Cisco usNIC BTL.

This BTL accesses the Cisco usNIC Linux device via the Linux verbs
API via Unreliable Datagram queue pairs.  A few noteworthy points:

 * This BTL does most of its own fragmentation; it tells the PML that
   it has a very high max_send_size (much higher than the network
   MTU).
 * Since UD fragments are, by definition, unreliable, the usnic BTL
   handles all of its own reliability via a sliding window approach
   using the opal_hotel construct and many tricks stolen from the
   corpus of knowledge surrounding efficient TCP.
 * There is a fun PML latency-metric based optimization for NUMA
   awareness of short messages.
 * Note that this is ''not'' a generic UD verbs BTL; it is specific to
   the Cisco usNIC device.

r28880 [[BR]]
Add some notes about the Cisco usNIC BTL.

r28907 [[BR]]
Use the RTE framework instead of calling ORTE directly.

Brian (rightfully) hit me on the head with the
don't-use-ORTE-use-the-rte-framework clue bat; the usnic BTL now
nicely plays with the RTE framework.

r28937 [[BR]]
Use sysfs to check MPI has enough VFs, QPs, and CQs
    
Use the new sysfs files to check that there are enough VFs, QPs, and
CQs for all the MPI processes on this server.
    
Move the checking code into its own subroutine to make it smaller and
easier to read/grok.