sysutils/debootstrap: Update to 1.0.128-2

For a debian-native package, a +nmuX version should be considered a new
upstream version (it just means "non mantainer upload" there). Derive
some PORTVERSION from that that's sane for our versioning.

While here, eliminate hardcoded /usr/local from Makefile patch.

Approved by: nc (maintainer), tcberner (mentor)
Differential Revision: https://reviews.freebsd.org/D38670