Install swift keystone extras requirements

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
(cherry picked from commit 04b0b61557)
(cherry picked from commit 90651cb1a9)

lib/swift

@@ -738,7 +738,9 @@ function init_swift {
 
 function install_swift {
     git_clone $SWIFT_REPO $SWIFT_DIR $SWIFT_BRANCH
-    setup_develop $SWIFT_DIR
+    # keystonemiddleware needs to be installed via keystone extras as defined
+    # in setup.cfg, see bug #1909018 for more details.
+    setup_develop $SWIFT_DIR keystone
     if [ "$SWIFT_USE_MOD_WSGI" == "True" ]; then
         install_apache_wsgi
     fi