Remove dnspython deprecation warning

[tripleee]

Where previously we used dns.resolver.query(), switch to d.r.resolve()

Complete compatibility would require d.r.resolve(search=True) but this works without it so far.

Perhaps see also rthalley/dnspython#581

[makyen]

This has dependencies and interrelated issues.

IIRC, the primary issue surrounding this was that the replacement for the deprecated function wasn't available in a dnspython version which is compatible with Python 3.5. So, fixing this issue requires:

• We stop supporting 3.5 (which we can now). This was mostly waiting for Python 3.9.0 to be released, which happened about a month ago.
  • Our officially supported versions and test structure should migrate to testing 3.6, 3.7, 3.8, and 3.9. This should be done in a separate PR.
  • We are considering removing CI testing being done by Travis, due to Travis changing how they handle open source projects (basically Travis is changing to make it a pain in the rear to use them). We should go ahead and do this for the SmokeDetector repository. Migrating the userscripts repository is something I've planned. We should also consider migrating the Metasmoke repository away from Travis. We would then still have the ChatExchange repo, which would need to be looked at. However, everything other than SD has a much lower CI volume requirement and may be reasonable to support on Travis for a while.
    Again, this should be a separate PR.
• We need to change the requirements.txt file to indicate a minimum version for dnspython which has the replacement function.
  • Updating requirements and switching to code that requires a new version means that such update must be coordinated with all current SmokeDetector runners, so we don't kill active or standby instances.

[makyen]

See previous comment.

[tripleee]

Related: #4514 #4841

[teward]

Complete compatibility would require d.r.resolve(search=True) but this works without it so far.

I'm curious, but why would we need search=True to make things work right? search uses local search domains as set by the system which for SmokeDetectors should be none.

From the DNSPython configuration documents, this is what 'search' does:

search, a bool or None, determines whether the search list configured in the system’s resolver configuration are used for relative names, and whether the resolver’s domain may be added to relative names.

We won't need search=True configured for our resolutions, because none of them are system-domain-local.

Therefore, that function being added or not is irrelevant, I just tested the difference between .resolve and .query for our code locally and for searches for websites it will not affect the searches.