add install_devstack_tools

An initial install for devstack-tools, this will need to use all the
fun pip extra variables for installation, however the current
pip_install always prefers python2, and we only want to do python3
here.

Change-Id: I3dcdb35130f76fad81cb7b0d4001b7e96efbbd84

inc/python

@@ -374,6 +374,13 @@ function install_python3 {
     fi
 }
 
+function install_devstack_tools {
+    # intentionally old to ensure devstack-gate has control
+    local dstools_version=${DSTOOLS_VERSION:-0.1.2}
+    install_python3
+    sudo pip3 install -U devstack-tools==${dstools_version}
+}
+
 # Restore xtrace
 $INC_PY_TRACE