sslutil: make cert fingerprints messages more actionable
The previous warning and abort messages were difficult to understand.
This patch makes them slightly better.
I think there is still room to tweak the messaging. And as we adopt
new security defaults, these messages will certainly change again.
But at least this takes us a step in the right direction.
References to "section" have been removed because if no fingerprint
is defined, "section" can never be "hostfingerprints." So just print
"hostsecurity" every time.
#require docutils gettext
$ $TESTDIR/check-gendoc da
checking for parse errors