Call ttse_terminate() when TTS engine is changed

Call ttse_terminate() when TTS engine is changed

- Previously, when TTS engine is changed, TTS clients call unprepare() and prepare() in order to connect to a new TTS engine.
In this case, dbus primary owner issue is occurred, because some clients request prepare() before the old TTS engine is terminated.(timing issue)
To solve this issue, we make TTS engine terminated by itself with calling ttse_terminate().
When TTS engine is terminated, all TTS clients can receive SERVICE_RESET and try to reprepare for the new TTS engine.
This can solve the dbus primary owner issue.

Change-Id: I431677f58f76322b6751cfbbf24009073fd35fc6
Signed-off-by: sooyeon <sooyeon.kim@samsung.com>