ServiceBus: Implement Renew-Lock for Message

Fixes (implements) #1271 
Source documentation on MSDN: [Renew-Lock for Message from Queue (Non-Destructive Read)](http://msdn.microsoft.com/en-us/library/jj839741.aspx).
Style and test coverage are largely taken from the &quot;UnlockMessage&quot; function implementation.
Tests pass OK against a real Azure service bus (with NOCK_OFF=&quot;true&quot;); I guess it won't be helpful to commit my own NOCK http recordings for the case.
CLA signed and emailed.<p><a href="https://github.com/Azure/azure-sdk-for-node/pull/1278">https://github.com/Azure/azure-sdk-for-node/pull/1278</a></p>
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