http: Add missing json import.
http: Add missing json import.

This is used in the exception handler for APIError.

henn/hil_sahil,lokI8/haas,meng-sun/hil,kylehogan/haas,apoorvemohan/haas,kylehogan/hil,apoorvemohan/haas,henn/hil,henn/hil_sahil,SahilTikale/haas,henn/hil,kylehogan/hil,SahilTikale/switchHaaS,meng-sun/hil,henn/haas,CCI-MOC/haas