Update to libmodulemd 2.2.0
    
    * Support for RPM checksums
    * Adds a new directive: "buildafter" for specifying build dependencies
    * Adds a new directive: "buildonly" to indicate that a component's built artifacts should be listed in the "filter" field.
    * Deprecate lookup functions by NSVC in favor of NSVCA (including the architecture.
    
    Signed-off-by: Stephen Gallagher <sgallagh@redhat.com>