Using @ as test seperator

Changed separator of multiple tests in single property file from . to @

So you will have

```
atomiclong@threadcount=10
atomiclong@class=com.bla.AtomicLongTest

atomicboolean@threadcount=10
atomicboolean@class=com.bla.AtomicBoolean
```

This functionality is needed to work with nested properties:

```
atomicboolean@address.street=foobar
atomicboolean@class=com.bla.AtomicBoolean
```