Revert "[CS] Remove check for UniMRCP SYNTHSTATUS"

This reverts commit 48ab4dccb0655c208a93459629d0568576eddf17.
[BUGFIX] Complete asterisk output with an error if PLAYBACKSTATUS is 'FAILED'
[BUGFIX] Account for PLAYBACKSTATUS in prompt also
Merge pull request #150 from adhearsion/feature/unimrcp_failure_check

Detect UniMRCP failure