get_latest_image_version_rpm(): ignore non-distro
get_latest_image_version_rpm(): ignore non-distro

This function is only used in distro kernel codepaths. Remove a similar
block of code from need_to_install_distro() and use this function.

Signed-off-by: Zack Cerza <d7cdf09fc0f0426e98c9978ee42da5d61fa54986@redhat.com>

SUSE/teuthology,ceph/teuthology,caibo2014/teuthology,robbat2/teuthology,ktdreyer/teuthology,ivotron/teuthology,SUSE/teuthology,dreamhost/teuthology,dmick/teuthology,zhouyuan/teuthology,caibo2014/teuthology,SUSE/teuthology,ivotron/teuthology,dmick/teuthology,zhouyuan/teuthology,ceph/teuthology,robbat2/teuthology,dmick/teuthology,michaelsevilla/teuthology,ktdreyer/teuthology,michaelsevilla/teuthology,dreamhost/teuthology