Bugfixes for Dockerfile

[frankgx97]

Fix "No such file or directory: 'git'" on docker build;
Fix "No module named mtt" on container start.

[daviddavo]

I also have this problem

  Downloading https://files.pythonhosted.org/packages/e7/a7/4cd50e57cc6f436f1cc3a7e8fa700ff9b8b4d471620629074913e3735fb2/cffi-1.11.5.tar.gz (438kB)
    Complete output from command python setup.py egg_info:
    
        No working compiler found, or bogus compiler options passed to
        the compiler from Python's standard "distutils" module.  See
        the error messages above.  Likely, the problem is not related
        to CFFI but generic to the setup.py of any Python package that
        tries to compile C code.  (Hints: on OS/X 10.8, for errors about
        -mno-fused-madd see http://stackoverflow.com/questions/22313407/
        Otherwise, see https://wiki.python.org/moin/CompLangPython or
        the IRC channel #python on irc.freenode.net.)

[NoNamePro0]

Yeah, looks very good. Does not need more image size or other negative things.
This PR makes affect for the .dockerignore-File, the file was not used in the previous version!