testsuite infrastructure: change stap_run api

testsuite infrastructure: change stap_run api

Formerly, the stap_run tcl proc accepted a target stap script file
name both as its first argument, as well as in the general stap
argument list at the end.  It passed the former name as an extra file
name iff it existed in the $srcdir/$testdir.  Some tests happened to
use test names that matched files, so triggered this stap_run
heuristic, even if the .stp files were specified some other way.  This
led to extra stap arguments, leading to "unused $0/@0 ..."  warnings,
leading to test failures.

Now, stap_run never does anything clever with its first parameter - it
just uses it to construct the dejagnu test case id/name.  The .stp
file name (if any - if not using -e SCRIPT for example) is now
expected to be included by the testcase.exp as arguments at the end.