sysutils/nomad: Update to 0.7.1

Changelog is in:
https://github.com/hashicorp/nomad/blob/master/CHANGELOG.md

Additional port changes:

• Changed to DISTVERSION.
• Added LICENSE_FILE.
• Added ONLY_FOR_ARCHS_REASON (go crashes).
• Removed go version specifier in BUILD_DEPENDS (version is already sufficient).
• Improved formatting in do-build.

PR: 225737
Submitted by: jhixson@gmail.com (maintainer)
Approved by: tcberner (mentor, implicit)