Adds support for multiple onupdate hook URLs

[solsson]

Note however that build-contract doesn't really verify this at the moment. You have to manually check logs for onupdate-logging.

The good news is that build-contract does pass, sometimes, now. See #3.

Once the nodejs based test is re-enabled we'll support validation of that url at least. See #5.

[solsson]

Getting timeouts when running build-contract or compose:

example-nodejs-client_1  |     Timeout update on publish
example-nodejs-client_1  | 
example-nodejs-client_1  |       23 | 
example-nodejs-client_1  |       24 |     getUpdatePromise = optionalDescription => new Promise((resolve, reject) => {
example-nodejs-client_1  |     > 25 |       const timeoutId = setTimeout(() => reject(new Error('Timeout ' + optionalDescription)), 3000);
example-nodejs-client_1  |          |                                                 ^
example-nodejs-client_1  |       26 |       events.once('onupdate', body => {
example-nodejs-client_1  |       27 |         resolve(body);
example-nodejs-client_1  |       28 |         clearInterval(timeoutId);
example-nodejs-client_1  | 
example-nodejs-client_1  |       at setTimeout (onupdate-flow.spec.js:25:49)
example-nodejs-client_1  |       at Timeout.callback [as _onTimeout] (node_modules/jsdom/lib/jsdom/browser/Window.js:678:19)

Maybe the internal name resolution doesn't work when the nodejs test isn't in `depends_on´ but if I add it there we'd get a circular dependency. We'd have to use standalone service that logs onupdate requests, with http based access for assertions.

[solsson]

@atamon I've pushed yolean/kafka-keyvalue@sha256:69f319da481ca3dd4755d919ad57d9169237de9654f9523987cff885bb351c00 from dd3b37d and verified that repeated builds ('./build-and-push.sh` but ignore the build-contract failure) produces the same sha - though probably only on my machine.

[solsson]

@atamon I've pushed sha256:ea36ae32c81171ab453651c05f5e76b7eb3e69376df1cdce5f7f51d3ecec981a with improved logging, in particular human-readability and including URLs and offsets for failed onupdate requests. I've also bumped kafka libs to 2.1.1.

[solsson]

build-contract passes now (though sometimes not when running dockerized as in ./build-and-push.sh so I've pushed :latest now from master: yolean/kafka-keyvalue@sha256:06c9b5e9f0d389d8973d827179a3d405b7ad99a8b1beb89c0cafa2699061220c.