make java relation optional

[kwmonroe]

Don't report blocked on a java relationship. This should only affect the standalone hadoop-client charm, since the status updates are guarded with if not silent.

While I'm here, cleanup the readme for charmstore formatting and update the simple deployment test for xenial.

[johnsca]

Technically, this could affect layers that depend on this and don't set silent: True, such as flume-hdfs, but I don't think we updated anything but Apache Spark with the java relation version anyway.

TBH, I think that we should drop the silent flag and only modify the status if this is the top-level charm ('hadoop-client' == hookenv.metadata()['name']). We only needed the flag if Java was required for some charms but not others.

[kwmonroe]

Sounds good @johnsca. I deprecated the 'silent' layer option and only alter the status when we're deployed as hadoop-client.

[johnsca]

LGTM 👍