tests: use error_abort in places expecting errors

Most of the TLS related tests are passing an in a "Error" object to
methods that are expected to fail, but then ignoring any error that is
set and instead asserting on a return value. This means that when an
error is unexpectedly raised, no information about it is printed out,
making failures hard to diagnose. Changing these tests to pass in
&error_abort will make unexpected failures print messages to stderr.

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>