Since the introduction of I8f24b839bf42e2fb9803dc7df3a30ae20cf264
s-proxy is no longer able to launch as keystonemiddleware (listed under
test-requirements.txt) has not been installed.
keystonemiddleware is listed as extras requirements in swift
- e0d46d77fa/setup.cfg (L79)
Let's install swift keystone extra requirements also.
Closes-Bug: #1909018
Change-Id: I02c692e95d70017eea03d82d75ae6c5e87bde8b1