mkdir /data/misc/cameraserver for AVD's camera HALs

cameraserver from nyc uses cameraserver as its username.
thus this change is needed for AVD (android virtual device)'s
camera HAL which is attached to cameraserver to work as that
HAL writes some files to /data/misc/media. the backward compatibility
issue should be handled as separate changes. this approach is 
preferred for finer-grained security isolation.

Change-Id: If028667d62df8fcac634ff1001759c39703b00dd