[System tests] We should check if active_slaves list is emtpy in tests 3 in 1 rabbit failover

[Tatyanka]

To get real failure result we should check if active_slaves list is emtpy in tests 3 in 1 rabbit failover, according to last run test fail with :
Error Message

list index out of range

Stacktrace

Traceback (most recent call last):
  File "/usr/lib/python2.7/unittest/case.py", line 331, in run
    testMethod()
  File "/usr/lib/python2.7/unittest/case.py", line 1043, in runTest
    self._testFunc()
  File "/home/jenkins/venv-nailgun-tests-2.9/local/lib/python2.7/site-packages/proboscis/case.py", line 296, in testng_method_mistake_capture_func
    compatability.capture_type_error(s_func)
  File "/home/jenkins/venv-nailgun-tests-2.9/local/lib/python2.7/site-packages/proboscis/compatability/exceptions_2_6.py", line 27, in capture_type_error
    func()
  File "/home/jenkins/venv-nailgun-tests-2.9/local/lib/python2.7/site-packages/proboscis/case.py", line 350, in func
    func(test_case.state.get_state())
  File "/home/jenkins/workspace/8.0.system_test.ubuntu.ha_neutron_destructive/fuelweb_test/helpers/decorators.py", line 80, in wrapper
    result = func(*args, **kwargs)
  File "/home/jenkins/workspace/8.0.system_test.ubuntu.ha_neutron_destructive/fuelweb_test/tests/tests_strength/test_failover.py", line 311, in ha_neutron_test_3_1_rabbit_failover
    super(self.__class__, self).test_3_1_rabbit_failover()
  File "/home/jenkins/workspace/8.0.system_test.ubuntu.ha_neutron_destructive/fuelweb_test/tests/tests_strength/test_failover_base.py", line 1058, in test_3_1_rabbit_failover
    active_slaves[0].name)
IndexError: list index out of range

But should fail before this step, because we do not expect here empty list

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/238836

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/238836
Committed: https://git.openstack.org/cgit/openstack/fuel-qa/commit/?id=974c95ca1516e2809b2ea53259a15415a5fbc9e5
Submitter: Jenkins
Branch: master

commit 974c95ca1516e2809b2ea53259a15415a5fbc9e5
Author: Tatyana Leontovich <email address hidden>
Date: Fri Oct 23 11:33:45 2015 +0300

    Add assertion for length of active_slaves list

    We should assert that active_slaves list is not empty
    before try tp get some data from
    it by index in test 3_in_1_rabbit_failover

    Change-Id: I0aae748bbd76da9acc81709e38d34c43d5e06a94
    Closes-Bug: #1509244