Don't require modifying the source to purge vms

Use an ENV var to indicate if vms should be deleted or just report what
would be deleted rather than requiring people to modify the tool's
source

tools/purge_archived_vms.rb

@@ -4,7 +4,7 @@
 # Delete any records older than this:
 ARCHIVE_CUTOFF = Time.now.utc - 1.month
 # If true, do not delete anything; only report:
-REPORT_ONLY = true
+REPORT_ONLY = ActiveModel::Type::Boolean.new.cast(ENV.fetch("REPORT_ONLY", true))
 
 old_logger = $log
 $log = VMDBLogger.new(STDOUT)
@@ -36,6 +36,7 @@
 end
 
 $log.info("Completed purging archived VMs. #{REPORT_ONLY ? 'Found' : 'Purged'} #{archived} archived VMs.")
+$log.info("To cleanup archived VMs re-run with REPORT_ONLY=false #{$PROGRAM_NAME}")
 
 $log.close
 $log = old_logger