OCL: process termination hung workaround

http://build.opencv.org/builders/precommit_OCL-win64-vc10/builds/181/steps/test_core-plain/logs/stdio:

```
[----------] Global test environment tear-down
[==========] 2765 tests from 130 test cases ran. (118373 ms total)
[  PASSED  ] 2765 tests.

  YOU HAVE 192 DISABLED TESTS


command timed out: 60 seconds without output, attempting to kill
program finished with exit code 1
```