fate: Don't use files from SRC_PATH in the actual tests

If building out of tree, make sure the filter scripts are copied
into the build tree before running tests. This makes sure that
SRC_PATH doesn't need to exist on the remote system (or doesn't
need to exist at the same path).

Signed-off-by: Martin Storsjö <martin@martin.st>
fate: Add a --target-samples path parameter

This allows having the samples accessible via different paths
on the target and on the host.

Signed-off-by: Martin Storsjö <martin@martin.st>