Description of problem:
Sometimes the ci jobs fail to run the functional tests when doing the prefix startup, and they fail with:

 
19:15:08 not ok 8 basic.full_run: start everything at once
19:15:08 # (from function `helpers.equals' in file tests/functional/helpers.bash, line 49,
19:15:08 #  in test file tests/functional/basic.bats, line 126)
19:15:08 #   `helpers.equals "$status" '0'' failed
19:15:08 # RUNNING:lagocli start
19:15:08 # WARNING: current session does not belong to lago group.
19:15:08 # 2015-12-01 19:14:13,413 - root - INFO - Creating network lago_functional_tests
19:15:08 # 2015-12-01 19:14:17,934 - root - INFO - Starting VM lago_functional_tests_vm01
19:15:08 # libvirt: QEMU Driver error : monitor socket did not show up: No such file or directory
19:15:08 # 2015-12-01 19:15:04,689 - root - INFO - Destroying network lago_functional_tests
19:15:08 # 2015-12-01 19:15:08,351 - root - ERROR - Error occured, aborting
19:15:08 # Traceback (most recent call last):
19:15:08 #   File "/usr/bin/lagocli", line 528, in main
19:15:08 #     func(args)
19:15:08 #   File "/usr/bin/lagocli", line 85, in wrapper
19:15:08 #     return func(lago.Prefix(os.getcwd()), args)
19:15:08 #   File "/usr/bin/lagocli", line 93, in wrapper
19:15:08 #     return func(prefix, args)
19:15:08 #   File "/usr/bin/lagocli", line 106, in do_start
19:15:08 #     prefix.start()
19:15:08 #   File "/usr/lib/python2.7/site-packages/lago/__init__.py", line 594, in start
19:15:08 #     self.virt_env.start()
19:15:08 #   File "/usr/lib/python2.7/site-packages/lago/virt.py", line 138, in start
19:15:08 #     vm.start()
19:15:08 #   File "/usr/lib/python2.7/site-packages/lago/virt.py", line 756, in start
19:15:08 #     self._env.libvirt_con.createXML(self._libvirt_xml())
19:15:08 #   File "/usr/lib64/python2.7/site-packages/libvirt.py", line 3611, in createXML
19:15:08 #     if ret is None:raise libvirtError('virDomainCreateXML() failed', conn=self)
19:15:08 # libvirtError: monitor socket did not show up: No such file or directory
19:15:08 # 1 == 0

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