Add OSTree dependencies to pulp_installer
Ticket moved to GitHub: "pulp/pulpcore/2037":https://github.com/pulp/pulpcore/issues/2037
The pulp_ostree plugin needs some prerequisites, similarly to pulp_rpm https://github.com/pulp/pulp_installer/tree/master/roles/pulp_rpm_prerequisites.
The required packages to install are:
- ostree (a client application that enables management of OSTree repositories)
- ostree-libs (a library that enables pulp_ostree to run OSTree commands via python bindings)