Add shutdown hook

Fixes #444 

For each interrupted test suite:
* mark each unfinished test case (but started) as broken with message `Test was interrupted` ![2014-12-08 16 38 31](https://cloud.githubusercontent.com/assets/2149631/5340033/c88b58b4-7ef8-11e4-9967-4c869a5e640d.png)
* add for each unfinished (but started) test suite warning `Test suite was interrupted, some test cases may be lost` (using fake broken test case) ![2014-12-08 16 38 19](https://cloud.githubusercontent.com/assets/2149631/5340030/c48ab62e-7ef8-11e4-986c-04ed9be544a5.png)
* write test suite results as usual 

but we **still lose info** about:
* all step & attachment data from interrupted test cases
* unstarted test case
* unstarted test suites