Increase timeout for the `test_external_volume` test (#6410)
Increase timeout for the `test_external_volume` test (#6410)

This test is flaky due to a rexray issue - see more in MARATHON-8348. Seems that we can't do more then wait longer for the task to eventually succeed until the actual problem is fixed.

JIRA: MARATHON-8348
mesosphere/marathon,gsantovena/marathon,gsantovena/marathon,mesosphere/marathon,gsantovena/marathon,gsantovena/marathon,mesosphere/marathon,mesosphere/marathon,mesosphere/marathon,gsantovena/marathon