Implement unit test for CSS version string handling (DM-1621).

There are two unit test actually, one on C++ side implemented as few
additional checks in css/testFacade, and one on python side in
admin/tests/test_cssVersion.py. Tests needed few additional changes to
other classes:
- QservAdmin constructor now takes either connInfo or config argument,
  this is passed directly to KvInterface.newImpl. This makes it possible
  to test QservAdmin against in-memory data, no Zookeeper needed.
- C++ class css/Facade has new static method which returns version
  number. This is useful for tests only, other clients should not need
  to care about versions.
- testKvInterfaceImpl and testFacade were added to the list of unit
  tests that we run at build time.
- Python class KvInterfaceMem (in css/python/kvInterface.py) has few
  fixes to  make it compatible with KvInterfaceZoo and
  KvInterfaceImplMem.
Minor cleanup for variable names defining version number.

Also use booss::lexical cast to convert integer version number into
its string representation instead of defining them separately.
Merge branch 'u/salnikov/DM-1621'