In python3 the functionality to import modules has been changed and
this broke the capability to add runtime tests from other layers.
This commit returns this capability to testimage and testexport.
[YOCTO #9705]
(From OE-Core rev: a26f23d3ce8f7e9f59dbc9bf27516377fd7a0a6d)
Signed-off-by: Mariano Lopez <mariano.lopez@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>