ARI: bridges/{bridgeID}/addChannel: add roles parameter

Roles are now cleared with each entry into a bridge with addChannel.
If the roles parameter is present, the role specified will be applied
to all channels being added with the addChannel command.

(closes issue ASTERISK-21973)
Reported by: Matt Jordan
https://reviewboard.asterisk.org/r/2691/


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@396182 f38db490-d61c-443f-a65b-d21fe96a405b