Only have pyximport installed while importing test modules
Only have pyximport installed while importing test modules

Fixes an issue where some module builds were being attempted at load
time. This was a problem for cassandra/numpy_parser, which requires a
header file not necessarily on the inlucde search path.

PYTHON-398

thelastpickle/python-driver,datastax/python-driver,kishkaru/python-driver,mobify/python-driver,vipjml/python-driver,coldeasy/python-driver,thobbs/python-driver,mambocab/python-driver,kishkaru/python-driver,thobbs/python-driver,markflorisson/python-driver,stef1927/python-driver,beobal/python-driver,jregovic/python-driver,yi719/python-driver,tempbottle/python-driver,coldeasy/python-driver,mobify/python-driver,jfelectron/python-driver,beobal/python-driver,mambocab/python-driver,tempbottle/python-driver,yi719/python-driver,markflorisson/python-driver,jregovic/python-driver,vipjml/python-driver,thelastpickle/python-driver,jfelectron/python-driver,stef1927/python-driver,datastax/python-driver