cl20: Reuse test harness code in headers (#255)

Some of the setup functionality is already there in the test harness, so
use that and remove the duplicated code from within the suite.

Signed-off-by: Radek Szymanski <radek.szymanski@arm.com>

test_conformance/headers/test_headers.c

@@ -655,5 +655,5 @@ int main(int argc, const char** argv)
 {
     log_info( "\nChecking operations on cl_types.\nNumbers, where presented, should walk upward from 0, with step of 1:\n" );
 
-    return parseAndCallCommandLineTests( argc, argv, NULL, test_num, test_list, true, 0, 0 );
+    return runTestHarness( argc, argv, test_num, test_list, false, true, 0 );
 }