Pin DIB to Python 2 compatible version on py2 jobs

Diskimage-builder dropped Python 2 support in 3.0.0. We need to pin the
-py2 jobs to a Python 2 compatible version. We set to 2.30.0 as per
latest upper-constraints.txt [1].

Note that Python 3 devstack installs will also have to be pinned to same
version because stable/stein devstack ensures that all libs being used
for development are installed under both versions of Python [2].

[1] https://opendev.org/openstack/requirements/src/commit/4ae10f52cec8f6d870c7d862d22c66a64ce74f9f/upper-constraints.txt#L612
[2] https://opendev.org/openstack/devstack/src/commit/ab86ced64cb6c053cf3340ab4d8a1d988a6b76c4/inc/python#L379-L388

Change-Id: Ib9954b8d634fc791e8cf0da73ad76ac8ff3e85b8
1 file changed