Make sure @Param("") and empty params from command line work correctly

```
What steps will reproduce the problem?
1. Create a Benchmark with a field annotated @VmParam["", "-Dfoo=true"]
2. Run benchmark

What is the expected output? What do you see instead?

I'd expect it to succeed. It reports that it got no response from the worker,
sometimes with an error log saying that it cannot create a JVM and sometimes
without any error. It'd be nice to be able to have a VmParam not have to pass
an argument for some cases (e.g. "-XX:+UseG1GC").

The current work-around is to set -Dadhfajlsdhfasd=dlfkasdfasdfhasl instead of
the empty VM parameter.

What version of the product are you using? On what operating system?

HEAD on OS-X
```

Original issue reported on code.google.com by `Smokejum...@gmail.com` on 30 Jan 2012 at 4:35