Add integration-cli test

Docker-DCO-1.1-Signed-off-by: Guillaume J. Charmes <guillaume@charmes.net> (github: creack)
Preserve trailing slash even for relative paths

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Remove steps from TestBuildAddRelative that are broken because of WAD and update the logDone message to reflect the actual test

When we say "ADD somefile somedir", we're asking Docker to replace "somedir" with "somefile", so "ADD somefile ." doesn't make sense, while "ADD somefile ./" totally does (because we're asking Docker to put "somefile" into "." as "somefile").

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)