[ignore] git should ignore jars built by metadata extension

The jars I added to .gitignore are deposited in the `lib/user` folder when Dmitriy's metadata extension is enabled in `extensions/local.build.properties`:

```
# Metadata Storage
include.feature.metadata = true
# sleepycat backend
include.feature.metadata.sleepycat = true
```

(Hoping to use this small pull request to better understand git flow.)