Restore and clarify config_version functionality

This branch is intended as a portability fix. Some functionailty had
been inadvertently removed as unused, but testing revealed that it had a
purpose. Because the purpose was unclear, this commit restores the
functionality AND clarifies it in the script names and comments in
config_version.sh.

scripts/config_version-r10k.rb

@@ -1,3 +1,4 @@
+#!/opt/puppetlabs/puppet/bin/ruby
 require 'json'
 require 'socket'
 

scripts/config_version-rugged.rb

@@ -0,0 +1,25 @@
+#!/opt/puppetlabs/puppet/bin/ruby
+begin
+  require 'rugged'
+  require 'socket'
+rescue LoadError
+  t = Time.new
+  puts t.to_i
+else
+  environmentpath = ARGV[0]
+  environment     = ARGV[1]
+
+  # Get the hostname of the Puppet master compiling the catalog.
+  # Sometimes the hostname is the fqdn, so we'll take the first segment.
+  compiling_master = Socket.gethostname.split('.').first
+
+  # Get the path to the environment being compiled.
+  repo = Rugged::Repository.discover(File.join(environmentpath, environment))
+  head = repo.head
+
+  # First 12 characters of the sha1 hash of the newest commit.
+  commit_id = head.target_id[0...11]
+
+  # Show the compiling master, environment name, and commit ID.
+  puts "#{compiling_master}-#{environment}-#{commit_id}"
+end

scripts/config_version.sh

@@ -1,14 +1,35 @@
 #!/bin/sh
 
+# Usage
 if [ $# -ne 2 -o ! -d "$1" -o ! -d "$1/$2" ]; then
   echo "usage: $0 <environmentpath> <environment>" >&2
   exit 1
 fi
 
-ruby=ruby
+# For portability, identify a preferred ruby executable to use
+ruby() {
+  [ -x /opt/puppetlabs/puppet/bin/ruby ] \
+    && /opt/puppetlabs/puppet/bin/ruby "$@" \
+    || /usr/bin/env ruby "$@"
+}
+
+# Determine how best to calculate a config_version
+if [ -e $1/$2/.r10k-deploy.json ]; then
+  # The environment was deployed using r10k. We will calculate the config
+  # version using the r10k data.
+  ruby $1/$2/scripts/config_version-r10k.rb $1 $2
+
+elif [ -e /opt/puppetlabs/server/pe_version ]; then
+  # This is a Puppet Enterprise system and we can rely on the rugged ruby gem
+  # being available.
+  ruby $1/$2/scripts/config_version-rugged.rb $1 $2
+
+elif [ -x /usr/bin/git ]; then
+  # The git command is available.
+  /usr/bin/git --git-dir $1/$2/.git rev-parse HEAD
+
+else
+  # Nothing else available; just use the date.
+  date +%s
 
-if [ -x /opt/puppetlabs/puppet/bin/ruby ]; then
-  ruby=/opt/puppetlabs/puppet/bin/ruby
 fi
-
-"${ruby}" "$1/$2/scripts/code_manager_config_version.rb" "$1" "$2"