Feature 1631 startup changes

[artntek]

Changes to the startup checks (and associated tests):

• Fixed: some tests were passing incorrectly - the test expectation was a RuntimeException, but they were throwing a NullPointerException. However, this was interpreted as a pass because a NullPointerException IS a RuntimeException. Solved by checking for the specific Exception Message.
• Added logic to skip availability check for solr, if solr has never been configured before, since legacy deployments require metacat to be operational under these circumstances, so the operator can enter the correct properties in the admin pages
• Changed the solr check logic so it ensures the schema is retrievable, instead of simply relying on receiving an HTTP 200
• Removed implements ServletContextListener and associated annotations, since this will now be called from Jing's new MetacatInitializer class
• Renamed StartupRequirementsListener (and test) to StartupRequirementsChecker, since it's no longer a listener.