[WIP] Skip UNIX-specific tests so they don't break Windows builds.

This PR is meant for discussion rather than merging straight away.

Some of the existing tests are clearly UNIX specific. I have created a new test group for them and excluded it explicitly from the tests.
Should I
  * move the tests to the Integration group
  * Find a way to decide at runtime whether the test should be executed based on the current platform
  * or make them pass on windows as well
The issue is with the ProcessTool (in newUnregisteredTool) which will generate UNIX-specific commands. The command which it tries to execute is:

```
bash -c chmod +x /tmp/brooklyn-20140630-182227176-M38A.sh ; /tmp/brooklyn-20140630-182227176-M38A.sh < /dev/null ; RESULT=$? ; echo Executed /tmp/brooklyn-20140630-182227176-M38A.sh result $RESULT ; rm -f /tmp/brooklyn-20140630-182227176-M38A.sh < /dev/null ; exit $RESULT
```