res_stasis: Add progress indications to operations which perform media.

res_stasis: Add progress indications to operations which perform media.

This change fixes operations which did not account for the fact that they may
be executed on channels which have not been answered. These operations will
now indicate progress when invoked.

ASTERISK-23560 #close
ASTERISk-23560 #comment Reported by: Jan Svoboda

Review: https://reviewboard.asterisk.org/r/3495/
........

Merged revisions 413121 from http://svn.asterisk.org/svn/asterisk/branches/12

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@413122 65c4cc65-6c06-0410-ace0-fbb531ad65f3