Fix a small problem that prevented marathon full path from being properly built

[ensonik]

…properly built when the base url included a path.

As tested in the REPL, the fix will properly join base url's and paths:

  >>> urljoin("http://marathon.mesos", "v2/apps")
  'http://marathon.mesos/v2/apps'

  >>> urljoin("http://marathon.mesos/service/marathon/", "v2/apps")
  'http://marathon.mesos/service/marathon/v2/apps'

  >>> urljoin("http://marathon.mesos", "v2/apps")
  'http://marathon.mesos/v2/apps'

  >>> urljoin("http://marathon.mesos/", "v2/apps")
  'http://marathon.mesos/v2/apps'

  >>> urljoin("http://marathon.mesos:8080", "v2/apps")
  'http://marathon.mesos:8080/v2/apps'

  >>> urljoin("http://marathon.mesos:8080/", "v2/apps")
  'http://marathon.mesos:8080/v2/apps'

Care needs to be taken to include a trailing slash in the base URL when there is a path included.

  >>> urljoin("http://marathon.mesos/service/marathon", "v2/apps")
  'http://marathon.mesos/service/v2/apps' # This is wrong. Include trailing slash to fix.

[degemer]

Thanks for the PR @ensonik!
Could you add a special case when there is no trailing slash in the URL ? (and add a trailing slash in the code)
Something like:

if url[-1] != '/':
    url += '/'

[degemer]

Fix #2612

[degemer]

Sorry, my comment is probably not needed, merging.
Thanks again for your contribution @ensonik !