Building with a dockerfile in a location other than the build context directory

'docker build' cli allows one to specify an arbitrary file as the dockerfile for the build. This is done by using the '-f' option on the command line. For example: docker build -f test/test.dockerfile context/bigfiles. This enables an elaborate structure of code and build files, a necessity in complex project.

The bluemix ic plugin, however, doesn't support the '-f' option, and expects the dockerfile to be named 'Dockerfile' and be placed in the build context directory.

Please fix it.