updated unit tests for unit conversion to use new unified function
updated unit tests for unit conversion to use new unified function

anubhavvardhan/qutip,cgranade/qutip,zasdfgbnm/qutip,anubhavvardhan/qutip,qutip/qutip,qutip/qutip,cgranade/qutip,zasdfgbnm/qutip