Consider using dnscache for caching DNS requests

[bwateratmsft]

This came up from microsoft/vscode-docker#1292 originally. It seems like Node.js does DNS lookups every single HTTP request: nodejs/node#5893

Supposedly, this can be resolved by configuring a system-wide DNS cache, or using packages like dnscache.

Can docker-modem make use of that package, or make it an option, in order to reduce DNS traffic in things like the vscode-docker extension?

[karolz-ms]

Another approach is to leverage nodejs/node#9296 to retrieve TTL information about DNS records and not repeat the resolution until the record has expired.