added solaris fact detection for ansible_pkg_mgr

The fact for ansible_pkg_mgr is not detected for Solaris and it is not possible to use ansible_pkg_mgr in any playbook (overwriting with group_vars is not possible).

Thats why I added the detection of the Solaris package manager. It is svr4pkg for solaris 10 (and older) and pkg for Solaris 11. The pkg module is still pending in pull request #6522