Add the ability to simulate an unclean disconnect

[mattrpav]

It would be really handy to have an API call to simulate an unclean disconnect in order for the LW message to be triggered. This would also close a functionality gap between the FuseSource MQTT Java client, which has the ability to do this.

Please fill out the form below before submitting, thank you!

• Bug exists Release Version 1.1.0 ( Master Branch)
• Bug exists in Snapshot Version 1.1.1-SNAPSHOT (Develop Branch)

If this is a bug regarding the Android Service, please rasie the bug here instead: https://github.com/eclipse/paho.mqtt.android/issues/new

Reference: https://bugs.eclipse.org/bugs/show_bug.cgi?id=499935

[mattrpav]

Any feedback on this PR?

[jpwsutton]

PR Merged.