fix(dns-cache): update lookup call to include force IPv4 option

[fallenbagel]

Description

Forgot to pass in the forceIPv4 option in the this.lookup with the fix in #4. Also fixed an issue with the test where we were testing the IPv6 scenario without clearing previous cache.

In addition, also added process.nextTick around all dns.lookup callbacks to prevent user-callback exceptions from propagating into our internal Promise chain to ensure that .catch handles only real dns errors and not accidental cache updates thrown by a caller code (as further hardening).

[gauthier-th]

• Why process.nextTick and not setImmediate? IIRC setImmediate is a more standard way of running something for the next event loop, while process.nextTick is only used to do some edge-case optimizations.

• Both process.nextTick and setImmediate will introduce a small delay because it will end for the current event loop to finish. It shouldn't be that much but it can be a few milliseconds.

• to prevent user-callback exceptions from propagating into our internal Promise chain

  I get the point, but in this case shouldn't we just invert the order of our .catch and .then so our .catch doesn't catch the errors coming from the call of the callback in our .then?

[fallenbagel]

• Why process.nextTick and not setImmediate? IIRC setImmediate is a more standard way of running something for the next event loop, while process.nextTick is only used to do some edge-case optimizations.

• Both process.nextTick and setImmediate will introduce a small delay because it will end for the current event loop to finish. It shouldn't be that much but it can be a few milliseconds.

• to prevent user-callback exceptions from propagating into our internal Promise chain

  I get the point, but in this case shouldn't we just invert the order of our .catch and .then so our .catch doesn't catch the errors coming from the call of the callback in our .then?

So should I remove it entirely?

[gauthier-th]

LGTM