Add user specified cache path to cache protocol
|Reproduced by developer:
|Analyzed by developer:
I create a patch that add a cache_path option to cache protocol.
The reason for such option is that av_tempfile may fail on different android devices. (see https://trac.ffmpeg.org/ticket/5620).even with 4c9d1c6f9a8f166703dc0333b53f5dba8dc5b414 fix , it still failed on my mobile phone.That may be due to some permission issues on different android devices. It is impossible to cover all the corner cases on different android devices.