test_mix_states was corrected:

* test_mix_states ignores long (in time) responses
(external problems (networking problems, hardware problems and etc.) must be
ignored - this test is not testing things like this)
* logging level was fixed
(for elliptics v2.26)
logger messages were corrected for `test_helper.network` module
debug output was removed
tests cases were added back
test_mix_states was refactored:

* code duplication was removed
* comment was added
unnecessary stabilising weights was removed
some comments were added
mix_states test was updated:

* requests are checking more explicitly now
(checker not encapsulated in a class now)
* some more test documentation was added
* comments were corrected
Merge branch 'v2.26' into fix/mix_states-test
Merge pull request #57 from 'fix/mix_states-test'

test_mix_states was corrected and some small changes