Add DNSSEC checks

[jsf9k]

@echudow, please give me permission to write to the develop branch on echudow/trustymail and I'll merge in the latest from upstream and make the CI tests pass.

@IanLee1521 may also need write permission too. He is a frequent contributor to cisagov/pshtt, cisagov/trustymail, and 18F/domain-scan.

[echudow]

@jsf9k, I added you and @IanLee1521. Thanks for the help.

[jsf9k]

@echudow, I'm still not allowed to push to develop:

$ git push
Enumerating objects: 28, done.
Counting objects: 100% (28/28), done.
Delta compression using up to 8 threads
Compressing objects: 100% (16/16), done.
Writing objects: 100% (16/16), 4.36 KiB | 1.45 MiB/s, done.
Total 16 (delta 8), reused 0 (delta 0)
remote: Resolving deltas: 100% (8/8), completed with 3 local objects.
To github.com:echudow/trustymail.git
 ! [remote rejected] develop -> develop (permission denied)
error: failed to push some refs to 'git@github.com:echudow/trustymail.git'

[echudow]

@jsf9k, I added you as a collaborator on echudow/trustymail and it says that it invited you, but it says that it's waiting for you to accept the invite. You should be able to go to https://github.com/echudow/trustymail/invitations to accept the invite.

I also invited you to a private repo for building custom trust stores for use with pshtt and sslyze if you are ever interested in taking a look. It's focused on DoD, but the extra intermediate certs could be somewhat useful.

[jsf9k]

Thanks, @echudow. The email was in my person email account and somehow I missed it. I was able to push just now. I'll also take a look at the other repo.

[jsf9k]

Based on the results from a full run with the new code, I think this PR is ready to be merged. I can't approve the PR myself, though, since I created it. @echudow or @IanLee1521, can either of you approve this PR? After that we should be able to merge.