Re-order test-requirements.txt
Re-order test-requirements.txt

tox fails when Sphinx is installed before fuel-plugin-builder.  There's
probably a missing requirement somewhere but reverting the list fixes
the issue for now.

Change-Id: I34cef8a3834e5cfb32d8673a632a6c00abd9b45e

stackforge/fuel-plugin-influxdb-grafana,stackforge/fuel-plugin-influxdb-grafana,stackforge/fuel-plugin-influxdb-grafana,stackforge/fuel-plugin-influxdb-grafana