tests: make runtests check that disabled tests exists

[bagder]

... and error out if so. Removed '536' from DISABLED as there is no such
test file.

[cvengler]

Tested and works!

[MarcelRaad]

Hmm, not for the autobuilds at least. Every single autobuild is failing with "WARNING! Non-exiting test 594 in DISABLED!". But data/test594 does exist... 😕
Maybe it looks in the wrong directory depending on where it's called from?

[cvengler]

I only tried executing runtests.pl inside the tests directory. It probably assumes that $PWD is in the tests folder

[bagder]

I suspect @emilengler is right. I'll dig in soon.

[cvengler]

Another thing that supports my theory is that running make test on my system sets $srcdir to

srcdir=. /usr/bin/perl -I. ./runtests.pl -a -s 

where as Travis does

srcdir=../../curl-99.98.97/tests /usr/bin/perl -I../../curl-99.98.97/tests ../../curl-99.98.97/tests/runtests.pl -a -s -p 1 1139

In my envrionment . points to the repo root. I verified this by printing out my @files = glob($srcdir . '/*');

EDIT: Oh no wait, it actually points to the test dir -.-