Add manila into service mapping. So if we deployed the
manila service, we can get the endpoint of it by default.
Re-sort the service mapping by its' initial.
Change-Id: I88dbafbe34b0e95eff0b00d9260f1b7a6fc0db77
1. add magnum install into post_install.sh
2. add magnum into SUPPORTED_SERVICE_EPS and PREFIX_MAPPINGS
3. add magnum policy
Change-Id: I10d2d337331d8c4857f6e58331e545eead0bf26f