Use RunAction2 so that CloverBuildAction.owner may be transient.

Otherwise the serial form of the action will encode the enclosing build. Normally this is harmless if ugly (XStream uses a backlink). But under lazy loading with garbage collection and recreation of builds, sometimes this results in the action saving a complete copy of the build (just backlinking to itself, the action). Then this can eventually cause a `Run` to be loaded which has no parent `Job`. Mayhem results:
```
java.lang.NullPointerException
	at hudson.model.Run.getRootDir(Run.java:976)
	at hudson.plugins.clover.CloverPublisher.getCloverXmlReport(CloverPublisher.java:127)
	at hudson.plugins.clover.CloverBuildAction.getResult(CloverBuildAction.java:144)
	at hudson.plugins.clover.CloverBuildAction.getBuildHealth(CloverBuildAction.java:45)
```