Update cloud/docker: if the image name containes a repository, strip it.

When using repositories other than the main one at docker.io, the image name contains the repo name (which itself contains ":" as a separator between domain and port). We don't really care about it here, so just get rid of it before looking at the image name.
Merge pull request #4928 from mscherer/fix_doc

fix various typos in the documentation
Merge pull request #4927 from intellectronica/intellectronica/docker-identify-private-repos-backport

Update cloud/docker: if the image name containes a repository, strip it.
Fix behavior of urpmi module where it always return "changed"
even when a package is already installed, since urpmi will
always return 0 wether it install or not.
optionally use rpm python module instead of calling a
external executable, to avoid the cost of forking.
Since python-rpm is not automatically present, we still fallback
on the slower rpm fork method.