add a helper to set host for feature test.
add a helper to set host for feature test.

the hostname will be restored after test

Coursemology/coursemology2,xzhflying/coursemology2,Coursemology/coursemology2,harryggg/coursemology2,cysjonathan/coursemology2,harryggg/coursemology2,cysjonathan/coursemology2,BenMQ/coursemology2,Coursemology/coursemology2,xzhflying/coursemology2,Coursemology/coursemology2,BenMQ/coursemology2,Coursemology/coursemology2,xzhflying/coursemology2,Coursemology/coursemology2,cysjonathan/coursemology2,harryggg/coursemology2,Coursemology/coursemology2,BenMQ/coursemology2