logging: update initialization code to use the new LogConfig logic

logging: update initialization code to use the new LogConfig logic

Summary:
Replace the initLoggingGlogStyle() function with a more generic initLogging()
function that accepts a log config string to be parsed with parseLogConfig().

Reviewed By: bolinfest, yfeldblum

Differential Revision: D6342086

fbshipit-source-id: fb1bffd11f190b70e03e2ccbf2b30be08d655242