testcase: give more time for instance destruction.

During teardown, we sometimes have errors that processes are still
running after being stopped, something like:
    Fault: <Fault 91: 'STILL_RUNNING: TestTelegraf-0'>

This is because we only retried `slapos node report` two times, but
`slapos node report` tells supervisor to stop processes without
waiting and when processes takes time to stop, this is sometimes not
enough. Increase to retry up to 10 times by default.
4 jobs for fix/testcase_wait_for_report in 0 seconds
Status Job ID Name Coverage
  External
running SlapOS.SoftwareReleases.IntegrationTest-Jerome-WIP

41994:47:14

failed SlapOS.SoftwareReleases.IntegrationTest-Jerome-WIP

04:22:18

canceled SlapOS.SoftwareReleases.IntegrationTest-Jerome-WIP

failed SlapOS.SoftwareReleases.IntegrationTest-Jerome-WIP

04:19:17