support dry-run for mustache templates. Redmine #6739
tag mustace acceptance tests with story_id 5535
Merge branch 'redmine_6739'
cf_popen() generates an error message on distributions where ifconfig cannot be found during IPv6 discovery, affects RHEL 7
cf_popen() generates an error message on distributions where netstat et al cannot be found during monitoring probing, affects RHEL 7
Fix crash when package_add_command is missing.

When using packages promise and not defining 'package_add_command'
agent crashes. This fixes crash.