virlog: Refactor virLogParseOutputs

virlog: Refactor virLogParseOutputs

The problem with the original virLogParseOutputs method was that the way it
parsed the input, walking the string char by char and using absolute jumps
depending on the virLogDestination type, was rather complicated to read.
This patch utilizes virStringSplit method twice, first time to filter out any
spaces and split the input to individual log outputs and then for each
individual output to tokenize it by to the parts according to our
PRIORITY:DESTINATION?(:DATA) format. Also, to STREQLEN for matching destination
was replaced with virDestinationTypeFromString call.