oeqa/core/loader.py: Avoid importing tests with built-ins name

oeqa/core/loader.py: Avoid importing tests with built-ins name

If importing a test with the same name as a built-in module,
it will silently import the built-in and check for tests in
built-in module. This happened with syslog module in debian
based machines, so add a raise to avoid this behavior.

[YOCTO #10978]

Signed-off-by: Mariano Lopez <mariano.lopez@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>