Disconnect the mediaplayer when reset

When the mediaplayer is reset the strong pointer to the
media service client is destroyed and the client should
deconstruct. However this could take some time and if a new
client is connected before the old client is disconnected
there could be problems. By assuring that the client disconnects
these problems can be avoided.

Change-Id: I5d2cf6d22860aa616b14397b1f523ddc35197b83