Adds $relayd->{dummyrun} and $client->{noclient} flags to relayd tests

Adds $relayd->{dummyrun} and $client->{noclient} flags to relayd tests
framework. These flags can be set from test file which eases performing
dry-runs of relayd long enough to do relayd.conf parsing, thus enabling the
grammar/parser-only tests.  While here, fix and improves args-http-mark.pl to a
correct use-case.

ok reyk