For #1634, refactor encoder process management.
For #1634, refactor encoder process management.

ossrs/srs,ossrs/srs,ossrs/srs,ossrs/srs,winlinvip/simple-rtmp-server,winlinvip/srs,winlinvip/srs,winlinvip/srs,ossrs/srs,winlinvip/srs,ossrs/srs,winlinvip/srs,winlinvip/srs