rtla/tests: Run runtime tests in temporary directory

rtla/tests: Run runtime tests in temporary directory

Create a temporary directory before each test case to serve as working
directory during the duration of the test.

This prevents littering of the original working directory as well as
allows tests to use it to avoid path conflicts.

In order not to break already existing tests, also add a new "testdir"
variable containing the directory where the test file is located. This
is then used to locate artifacts used during testing like BPF programs
and scripts for checking the tracer threads.

Link: https://lore.kernel.org/r/20260526102523.2662391-3-tglozar@redhat.com
Signed-off-by: Tomas Glozar <tglozar@redhat.com>