Bump next version to 1.7.4.1

Open stable/folsom by bumping next version to 1.7.4.1.

Change-Id: I68cf664b25b946095657f972a2550ad903ea9d86
Use pypi for python-swiftclient dependency.

Using github as a package source is less reliable in the Jenkins test
framework than using pypi. This is because the Jenkins test framework
has a local pypi mirror.

Change-Id: Ia904d39ce70f5c2bd7d6edb9172f8226131074e2