Bump python-savannaclient version to >=0.4.1

There are several reasons because we'd like to do it:

* it includes support for all features that'll be released in i-2;
* and, so, we'd like to use it to update Horizon plugin with new features;
* there are several fixes that blocks usage of client in Heat and Tempest;
* it contains basic implementation of CLI that we'd like to test in Tempest.

Change-Id: If46cbc1aeaa970b5b3d1066a83ea9b22f9d0ea49
Merge "Bump python-savannaclient version to >=0.4.1"