Change remap_hosts to accept dictionary

[zephraph]

remap_hosts should allow multiple hosts to be remapped at once. In order to achieve it should take a dictionary argument instead of a single url/address pair.

[zephraph]

Hopefully that's a bit better. I created an extra test and it's likely that one or both of the test function docstrings should be changed.

Just let me know if there's anything else I need to fix.

[zephraph]

@AutomatedTester how does everything look? Do you want me to squash my commits or make any other changes?

[AutomatedTester]

landed in 0e959d6