Update to jetty-9.4.x

[gregw]

This will provide access to:

• greatly improved session manager and gcloud/memcache integration
• more flexible request customizer
• improved performance

[gregw]

Progress report after testing again jetty-9.4.0.RC0:

• Update to latest version of google-cloud-java API. Update gcloud datastore to 0.3.0 jetty/jetty.project#931
• We noticed a very large dependency tree of google-cloud-java with duplicates and have opened Datastore: duplicate classes in dependencies googleapis/google-cloud-java#1278 to minimize this. However, even when minimal, the dependency list will be too cumbersome to hide using Jetty's existing Black-list classpath, so we have opened location based black/white classpath patterns jetty/jetty.project#963 to make hiding dependencies simpler.
• To achieve an initial "bug for bug" and backwards data compatibility the gae-compat session data store for jetty-gae-compat-runtime we need to expose a few more protected methods to avoid too duplicated code and create some modules for ease of configuration: Make GCloudSessionDataStore more configurable jetty/jetty.project#941, Make a NullSessionCache module jetty/jetty.project#944, Property for SessionCache.saveOnCreate missing in session-cache-hash.mod jetty/jetty.project#945
• For the jetty-runtime data store session manager, it is currently not possible to programatically create the indexes that are needed for more efficient and correct session expiry. Thus we need to be able to run in a fallback mode that is less efficient if the indexes have not been created: Fallback to less efficient queries if no indexes for GCloudSessionDataStore jetty/jetty.project#954
• It is unclear if versions deployed within the one gcloud project will be heterogeneous or homogeneous, so it is unclear how sessions should be partitioned (if at all). For future flexibility we will add name space support: Add namespace support to GCloudSessionDataStore jetty/jetty.project#953

We are on track to implement most of these enhancements this week to produce a 9.4.0.RC1 next week, which we can again test integrate.

[jmcc0nn3ll]

@meltsufin can we consider this one closed now? master is on 9.4

[meltsufin]

@jmcc0nn3ll Yep, upgrade to 9.4 completed via #90.