modified the dockerbuild and git archive feature

* dockerbuild now has support to using a secure connection to the docker host if
  the docker API is listening on a public interface. Username and password must
  be given in this case.
* dockerbuild now adds git repositories as archiv file, as this is easier to
  create and handle (docker will automatically extract archives added).
* cleaned up the git adaptor a lot: using a bare repository.
fixed bug with connection

Using the generic http connection doesn't work when in tunnel mode. Must always
use the dedicated http client.
added support for bundler optimization

To only run bundler if really necessary the follow hack is used:
* Gemfile and Gemfile.lock are added to the docker archive in their respective
  latest revision.
* Bundler is run on these files.
* Only afterwards the actual source is extracted.

This way the bundling is only run if necessary.

The dockerbuild.Build struct now has a RubyProject flag, that will add the
required files for the locking.

The git helper library was modified to support adding files in specific
revisions (setting the modification time accordingly).
read hostconfig from docker api

This has information on exported ports.