testing/testcase: (re) start slapos in setUpModule

Slapos is started the first time the StandaloneSlapOS is instanciated,
then, in each class teardown we stop slapos, so the second time
setUpModule is executed, the slapos is not started yet.

Start it one more time in setUpModule to ensure it's started in this
scenario.

slapos/testing/testcase.py

@@ -331,6 +331,8 @@ def installSoftwareUrlList(cls, software_url_list, max_retry=2, debug=False):
       cls._copySnapshot(standalone_log, name)
 
   try:
+    cls.logger.debug("Starting")
+    cls.slap.start()
     for software_url in software_url_list:
       cls.logger.debug("Supplying %s", software_url)
       cls.slap.supply(software_url)