Refactor to fix spotbugs identified issues

[willwh]

Running mvn spotbugs:check against the plugin, there are a number of issues that we should likely address.

There is also a comment from @slide in Jenkins JIRA;

You may want to use req.bindJson rather than looking at the JSON data directly.
https://github.com/vipinsthename/environment-dashboard/blob/master/src/main/java/org/jenkinsci/plugins/environmentdashboard/DashboardBuilder.java#L342 and here https://github.com/vipinsthename/environment-dashboard/blob/master/src/main/java/org/jenkinsci/plugins/environmentdashboard/EnvDashboardView.java#L232