Support message buffering before initial connect

[nofarius]

The codeformatting changes to develop caused code conflicts in PR #198. This is the same PR but with the code conflicts removed. All code changes should be attributed to @matsukaz as he was the original contributor. Submitting a new PR as I don't have access to update the original PR

This should resolve issue #197

Original PR description

This change will enable offline buffering even if initial connection has never been established yet.

I've changed MqttAndoidClient, MqttService, MqttConnection in order to instantiate these instances before connection get established.

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[matsukaz]

@nofarius Thank you for creating this PR!
I had no time to check my code to see why the code conflicts.
Hope this PR get merged.

[nofarius]

@matsukaz no problem, looking forward to this functionality being part of this project!

Unfortunately, there are some unit tests that are not working. I have managed to resolve one of them, which I haven't committed yet as it then caused others to break....

Basically, it has to do with the removal of the clientHandle cleanup in MqttAndroidClient and MqttService files, which means that the connectOptions are persisting between connect / disconnect cycles. See the testCleanSession test, where cleanSession is being changed in the connectOptions, but the original value is still being used.

If you're able, I would appreciate your contribution to reviewing these unit tests. I have added you as a collaborator to the https://github.com/nofarius/paho.mqtt.android project, pushing to the msg_buffer_before_connect brach should update this PR

[nofarius]

Since it is not possible to enable / disable network connection inside a unit test (as far as I'm aware), I have added an Enable Message Buffer option to the sample app so that testing message buffer while app is offline (eg airplane mode) can be done manually

[nofarius]

Is there a known issue with the unit tests randomly failing when they should pass?

I can't replicate the test failure in the auto build locally. When I run the whole test suite locally usually they all pass, and sometimes random tests fail for no real reason... I then run the test suite again and the same test that failed then succeeds with no code changes...