Point external nng reference for reconnect fix

Point external nng reference for reconnect fix

Begin using NNG commit e618abf8f3db2a94269a79c8901a51148d48fcc2
in order to pick up the fix for NNG bug:
  #970 TCP connections through docker-proxy do not reconnect

Change-Id: I367ea489ff86519c17a357ff9415a873e14e1f1e

Changes to incorporate new NNG conn shut error

NNG added a connection shut error when the reconnection through
proxy bug was fixed.  This change catches the new state and
sets the status in the message accordingly.

Small tweak to application tests to prvent timing issues
when running in jenkins verification environment.

Signed-off-by: E. Scott Daniels <daniels@research.att.com>
Change-Id: Idaf98feb6c7b5724f1cceab8ba051bb5fccd7a7e