refpolicy: bump to 2.20170805

refpolicy: bump to 2.20170805

In addition to a simple bump, the following extra changes have occured:
  - Change the refpolicy site to the official release URL.
  - Remove REFPOLICY_SITE_METHOD and REFPOLICY_GIT_SUBMODULES as the contrib
    submodule is included in the release tarball.
  - Refpolicy is now compatible with python3, as such, remove host-python.
    from the dependencies and add a check for python3 or python in it's place.
  - Add upstreamed 0001-fix-regex-escape-sequence-error.patch to fix building
    against python3.6.
  - Add sha256 license hash to hash file.

Signed-off-by: Adam Duskett <Adamduskett@outlook.com>
Tested-by: Matt Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>