Acceptance-tests: Fix 'verify: false' bug

Sporadic unit tests failures are caused by long withstanding bug in Jcraft
SSH library.  Despite announcements in the release notes for the versions
0.1.50 and 0.1.51 of this library, claiming that this bug was fixed, that
bug still exists and can be easily reproduced.

This change introduces an unit test, that reliably reproduces the
'verify: false' bug in one test method (that is running against
established SSH port number, so that random port assignments can be
eliminated as the reason for the sporadic unit test failures).

The workaround introduced in this change is to conditionally use
bouncycastle library. Per default bouncycastle library is used. To run unit
tests without it, set NO_BOUNCYCASTLE library to any value:

  NO_BOUNCYCASTLE=1 buck test --all

Change-Id: I9d5fdf992082b3658542d84ed9551ac2bf146414
Merge "Acceptance-tests: Fix 'verify: false' bug"