Camera: Add debug code to dump JPEG images

- Debugging can be turned on by running:
adb shell cmd media.camera set-image-dump-mask 1
- Current flag setting can be queried by:
adb shell cmd media.camera get-image-dump-mask
- JPEG images are stored in /data/misc/cameraserver
- Image name is in the format of:
IMG_[YYYY][MM][DD]_[HH][MM][SS]_[TIMESTAMP].jpg

Test: Run adb command, run StillCapture test, and check output files
Bug: 172365775
Change-Id: Iec573ab68dcf5752ff036733b83b4088da8199cb