Fix configure script for functional tests

The script was pinning oslo.config to 3.0.0, which does not work
now (deprecation error). Changed to not pin to a version and
elaborated on note as to why this needs to be there.

Change-Id: I970903983229e37dfc93dba396914a01fa5bc057

tools/configure_for_vpn_func_testing.sh

@@ -56,7 +56,9 @@ function configure_host_for_vpn_func_testing {
     if [ "$IS_GATE" == "True" ]; then
         configure_host_for_func_testing
     fi
-    sudo pip install --force oslo.config==3.0.0 # req for oslo-config-generator
+    # Note(pc_m): Need to ensure this is installed so we have
+    # oslo-config-generator present (as this script runs before tox.ini).
+    sudo pip install --force oslo.config
     _install_vpn_package
     _configure_vpn_ini_file
 }