avformat/hlsenc: temp_file usage for master playlist and vtt playlist

avformat/hlsenc: temp_file usage for master playlist and vtt playlist

currently master playlist and subtitle playlist creation does not use
temporary files even when temp_file flag is set. Most of the use cases
it is not a problem because master playlist creation happens once on the
beginning of the whole process. But if master playlist is periodically
re-created because of master_pl_refresh_rate is set, non-atomic playlist
creation may cause problems in case of live streaming. This patch
correct this behavior by adding this functionality.

Reviewed-by: Steven Liu <lq@onvideo.cn>
Signed-off-by: Bela Bodecs <bodecsb@vivanet.hu>