rpmkit.extras.listerrata_for_releases: add some logs in list_errata_from_rhns() to inform release dates computed
rpmkit.extras.listerrata_for_releases: make errata of newer release not contained
rpmkit.extras.listerrata_for_releases: add one more log in list_errata_from_rhns() to inform the period of errata to get
rpmkit.extras.listerrata_for_releases: add a link of the table of rhel releases and release dates
rpmkit.extras.listerrata_for_releases: preserve period in metadata