fix concurrency test

[ofrei]

No description provided.

[ofrei]

After fix:

H:\GitHub\bigartm\bigartm\python>py.test tests/wrapper/test_03_concurrency.py --verbose -s
============================= test session starts =============================
platform win32 -- Python 3.5.2, pytest-2.9.2, py-1.4.31, pluggy-0.3.1 -- C:\Program Files\Anaconda3\python.exe
cachedir: .cache
rootdir: H:\GitHub\bigartm\bigartm\python, inifile:
collected 1 items

tests/wrapper/test_03_concurrency.py::test_func Iter#0: Perplexity = 6710.208, Time = 0.678
Iter#1: Perplexity = 2434.135, Time = 0.657
Iter#2: Perplexity = 2202.418, Time = 0.673
Iter#3: Perplexity = 1936.493, Time = 0.660
Iter#4: Perplexity = 1774.600, Time = 0.679
Average time per iteration = 0.669
Iter#0: Perplexity = 6710.208, Time = 1.241
Iter#1: Perplexity = 2434.135, Time = 1.220
Iter#2: Perplexity = 2202.418, Time = 1.213
Iter#3: Perplexity = 1936.493, Time = 1.218
Iter#4: Perplexity = 1774.600, Time = 1.196
Average time per iteration = 1.218
Iter#0: Perplexity = 6710.208, Time = 1.999
Iter#1: Perplexity = 2434.135, Time = 2.083
Iter#2: Perplexity = 2202.418, Time = 2.017
Iter#3: Perplexity = 1936.493, Time = 2.030
Iter#4: Perplexity = 1774.600, Time = 2.023
Average time per iteration = 2.030