config_version scripts: commit-ID length mismatch, ruby() fallback flaw, ShellCheck warnings

[miharp]

Small cleanups in scripts/:

1. Comment/behavior mismatch — config_version-r10k.rb says "first 12 characters of the commit ID" but [0...11] returns 11 (verified output: host-production-abcdef12345). Use [0...12] or fix the comment.
2. Fallback can run a second interpreter — the ruby() helper in config_version.sh:

   [ -x /opt/puppetlabs/puppet/bin/ruby ] \
     && /opt/puppetlabs/puppet/bin/ruby "$@" \
     || /usr/bin/env ruby "$@"

   If the preferred Ruby exists but exits non-zero, the || branch runs env ruby on the same args too. Use an if/else.
3. ShellCheck warnings — obsolete -o compound test in the usage check, and unquoted $1/$2 path expansions.