Added Vultr DNS Scripts

[happytreees]

This PR will add Vultr DNS verification scripts to the repository.

Scripts use methods provided by the Vultr API:
https://www.vultr.com/api/#tag/dns

[happytreees]

Output of working scripts:

Check all certificates
ssltest.mytestdomain.com: no certificate obtained from host
Registering account
Verify each domain
Verifying ssltest.mytestdomain.com
checking DNS at ns1.vultr.com
sleeping 60 seconds before asking the ACME server to check the dns
sending request to ACME server saying we're ready for challenge
checking if challenge is complete
Verified ssltest.mytestdomain.com
Verifying www.ssltest.mytestdomain.com
checking DNS at ns1.vultr.com
sleeping 60 seconds before asking the ACME server to check the dns
sending request to ACME server saying we're ready for challenge
checking if challenge is complete
Verified www.ssltest.mytestdomain.com
Verification completed, obtaining certificate.
Requesting Finalize Link
Requesting Order Link
Requesting certificate
Certificate saved in /Users/mytestdomain/.getssl/ssltest.mytestdomain.com/ssltest.mytestdomain.com.crt

[timkimber]

@happytreees thanks for adding these scripts, so it's taken me so long to merge them!