As part of review [1] the openstack build system assumes the layout of
the docs directories to be doc/build. This is not what requests-mock was
producing. Fix the docs building directories to make it work with the
build system again.
[1] Icb0c02dc5b6f7b5e248e0df6d6093c29535b08f3
Closes-Bug: #1630114
Change-Id: Iea93ecfb0506d5ccd0b79ad35f5677797fadf730
9fbd45b35f