processActivity returns a promise that must be handled

[christopheranderson]

Describe the bug

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All process activity calls return a promise and, thus, need to be handled. Our current code patterns do not involve handling these promises leading to node.js WARNING messages. It will also cause restify to hang until socket timeout.

To Reproduce

Steps to reproduce the behavior:

1. Take any JS sample (echo)
2. Make the code inside process activity throw an error (manually inserting a throw into "processActivity" itself is the fastest)
3. restify will hang and node.js will issue a warning for an unhandled promise rejection.

Expected behavior

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We should .catch(next) or .then(next, next) all process activity calls in our code.

Screenshots

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Additional context

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[bug]