pkgbase: accommodate pkg < 1.17

6cafdee71d2b adapted the pkgbase build for 1.17, but broke Cirrus-CI's
use of PKG_FORMAT=tar (the quarterly package set still has pkg 1.16).
Because of this I disabled the pkgbase build and test in 2bfba2a04b05.

Now, check pkg --version and use the old logic for < 1.17.

To be reverted once we no longer encounter pkg 1.16 in Cirrus-CI (i.e.,
via GCP cloud images) to avoid keeping this extra complexity around.

PR: 257422
Reviewed by: manu
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D31324

(cherry picked from commit 4e224e4be7c37052567ec4cd2481f299487fc222)
(cherry picked from commit 4dbac528db6040694cd57c42a64e036daa91db86)
(cherry picked from commit 54247ce1f96f04d16f1429007bac3607c8a0a39e)