Updates the rxtx_factor validations in the instance_types modules so
that rxtx_factor is validated as a float. Given that rxtx_factor is stored
as a float in the database this makes sense... and also adheres
to some of the extension documentation as well (although some of
the extension docs were incorrect as well).
Previously rxtx_factor was being cast into an int which caused it to
be stored and displayed incorrectly via the API.
This patchset adds a test which fails with the old code.
Additionally some of the API docs are corrected so that rxtx_factor is
listed as a float in all examples.
Fixes LP Bug #1081287.
Change-Id: Iae98522a1f2ed63cbd2497b0b0af5ac2d9bb935c
a5e4818b0a