Added PCF command timeout

[andrewkirillov-ibm]

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What

Added command_timeout option to PCFExecute to control PCF command's expirty.

How

A new command_timeout is added to PCFExecute with a default value of 0. When it is set a 0 we behave as before the change, so nothing gets broken. In this case PCF command timeout/expriry is calculated automatically based on 'response_wait_interval. However, if command_timeout` is set explicitly, then its value is used.

Testing

Tested in a test application by setting the new command_timeout option.

Issues

Fixes #14

[ibmmqmet]

I'm not completely convinced by your description of the problem, as the command message doesn't "expire" during the processing of the responses. The command server should be sending back all of the responses with the same expiry - that which was remaining in the command when it was read. Which should be close to the 3x waitInterval as putting that single command and having it read by the command server ought to be relatively quick.

Though you're right that if it's taking a very long time to get all the responses, some might have expired before you get to them.

Depending on how you're using the reply queue, you might be able to take advantage of readahead to get responses sent to you faster in the background while you're still processing them.

Nonetheless, I've merged the PR into my local repo, as it doesn't do any active harm, and it'll get publicly merged when I do the next push from my machine.