DNS TXT JWT expiration should disconnect client

[schmidtw]

When the JWT acquired via the DNS TXT record expires, parodus should disconnect from the URL specified in that JWT and restart the reconnection process fresh.

This shall include attempting to acquire an updated DNS TXT record with a JWT. All normal & default semantics apply.

[bill1600]

pull request #189 (April 2018) created for this.
But it was never merged.
It will have to be brought up to date with current code.