Camera: Fix camcorder crash during pause and resume

When camcorder is suspended in background, if it receives resume
and pause event in very short interval, crash will happen.
After receiving resume event, the onresume method will be called,
and it will start another thread for starting preview. And soon,
the main thread receives pause event, the onpause method which will
close camera is called.
There will be a racing between the main thread and start preview
thread. If close camera get done first, crash will be observed.
To avoid the racing, the close camera operation should wait for the
start preview operation, and the join method is used here for
synchronization.

CRs-Fixed: 526007
Change-Id: Idf6a8660378bf1a65af1f5194a35d30822f1dcf6