release: fix pkg METALOG in Makefile

[ifreund_freebsdfoundation.org]

Summary

From my testing, none of the PKG_INSTALL invocations in release/Makefile
actually work currently due to pkg writing to the wrong METALOG file.

Since PKG_ARGS refers to the METALOG in the working directory, we must
be careful to run pkg from the directory containing the correct METALOG.

Sponsored by: The FreeBSD Foundation

[ifreund_freebsdfoundation.org]

Uh I'm not sure how I messed up my testing but this patch is incorrect, everything works fine since pkg interprets the METALOG option relative to the rootdir option.

Sorry for the noise.

[ifreund_freebsdfoundation.org]

Aha! The thing I was seeing happened again and I think I understand it now, submitted D50344.