Use uwsgi binary from path

All these uwsgi invocations assume that the uwsgi binary is in the
same directory as their project binaries are installed into (probably
/usr/bin).  That may not be correct -- for example if using a packaged
uwsgi on Fedora the binary will live in /usr/sbin/uwsgi (not /usr/bin
where the project files from pip are).

Switch invocations to just find it in the path.

Change-Id: I298e3374e9c84e209ffcabbaaacda17f8df19f4f
diff --git a/lib/neutron b/lib/neutron
index 9e6a80c..885df97 100644
--- a/lib/neutron
+++ b/lib/neutron
@@ -463,7 +463,7 @@
     done
 
     if [ "$NEUTRON_DEPLOY_MOD_WSGI" == "True" ]; then
-        run_process neutron-api "$NEUTRON_BIN_DIR/uwsgi --procname-prefix neutron-api --ini $NEUTRON_UWSGI_CONF"
+        run_process neutron-api "$(which uwsgi) --procname-prefix neutron-api --ini $NEUTRON_UWSGI_CONF"
         neutron_url=$service_protocol://$NEUTRON_SERVICE_HOST/networking/
         enable_service neutron-rpc-server
         run_process neutron-rpc-server "$NEUTRON_BIN_DIR/neutron-rpc-server $opts"