cdma_ruim: Fix unit tests and actually enable them

As pySim.cdma_ruim was not imported by test_files.py, the unit tests
were apparently never executed and hence didn't pass.  Let's fix both
of those problems.

Change-Id: Icdf4621eb68d05a4948ae9efeb81a007d48e1bb7

tests/test_files.py

@@ -29,6 +29,7 @@ import pySim.ts_31_103
 import pySim.ts_51_011
 import pySim.sysmocom_sja2
 import pySim.gsm_r
+import pySim.cdma_ruim
 
 def get_qualified_name(c):
     """return the qualified (by module) name of a class."""