Add support for Python for skaffold debug

[briandealwis]

Add support for debugging Python 2.7 and 3.7 applications. These language runtimes require additional debugging support files that will be installed via the "duct-tape" image defined by the container-debug-support project.

The Python language debugging support currently installs ptvsd, which provides a debug adapter for Python. It remains to be seen if this is sufficient for use with IntelliJ.

[briandealwis]

Although IntelliJ/PyCharm does use pydevd, which is wrapped by ptvsd, ptvsd doesn't seem to expose its pydevd and may have some problems co-existing with another version of pydevd installed alongside.

We likely will need to support some kind of runtime flavour. So IntelliJ could launch skaffold debug --flavour ij and match a python-ij runtime. Perhaps the dab (Debug Adapter Protocol) could be a default flavour.

[briandealwis]

NB: for ptvsd, I needed to configure a path mapping in my launch parameters:

{
  "pathMappings": [ 
    {
      "remoteRoot": "/app" , 
      "localRoot": "/Users/bsd/go/src/github.com/GoogleContainerTools/skaffold/integration/testdata/debug/python3" 
    }
  ]
}