Add an option to not fail the build if checks timed out

[zaza]

Currently if defined checks time out an exception is thrown from the plugin causing the build to fail. We would like the build to be marked as unstable in this case, which would happen further down the line if only the build kept going. The "timed out" exception stops the build execution.

[zaza]

We did try using the Text Finder plugin to mitigate the issue, but it cannot change the build status from Failure to Unstable because "build results cannot be improved".