MFC r352520 (partial):

MFC r352520 (partial):
 The original commit was a direct commit to stable/12, as at the time it
 was presumed it would not be necessary for head.  However, when it is
 time to create a releng branch or switch from PRERELEASE/STABLE to
 BETA/RC, the pkg(7) Makefile needs further adjusting.  This commit
 includes those further adjustments, evaluating the BRANCH variable from
 release/Makefile to determine the pkg(7) repository to use.

Approved by:	re (kib, insta-MFC)
Sponsored by:	Rubicon Communications, LLC (Netgate)