oeqa/runtime: search sys.path explicitly for modules

The controller module loading code needs to be told what directories
to search for modules via the target_modules_path keyword argument, which
is set to BBPATH.

However, as the actual module loading is done via importlib this relies
on the paths being on sys.path, which it is as base.bbclass puts each
layer's lib/ in sys.path.

Simplify the code by removing this indirection, and simply search
sys.path directly.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>