Clean up app_mysql's application entry points to properly parse arguments

When parsing arguments, application entry points should not attempt to
directly modify the parameters to the function. This patch properly duplicates
the passed in parameters before attempting to parse them.

(issue ASTERISK-20658)
Reported by: wdoekes
patches:
  issueA20658_sanitize_app_mysql.patch uploaded by wdoekes (license 5674)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@378384 65c4cc65-6c06-0410-ace0-fbb531ad65f3