use rspec-expectations 3.x for test harness

adapt to breaking changes in rspec-expectations 3
https://www.relishapp.com/rspec/rspec-expectations/v/3-0/docs/changelog
rspec/mocha now requires symbol for mock_with

Resolves error:

    Unknown mocking framework: "mocha".
    Pass a module or one of [:rspec, :flexmock, :rr, :mocha, :nothing]
run spec_standalone to support old and current rake tasks

Latest bundle seems to not invoke :spec_standalone from :spec,
so invoke it directly. This ensures the harness runs regardless
of which bundle is installed.
add tools to work with mercurial repositories
update all packages in base image at build-time
add host and dig commands to devenv
add ftp and tftp clients

These are useful for testing other services.
use the "semi-official" fedora 20 base image
support "nil" value in docker-api of test harness