virlog: Refactor virLogParseFilters
virlog: Refactor virLogParseFilters

Patch 0b231195 refactored logging output parser to make it more readable.
This patch does similar thing to logging filter parser.

olafhering/libvirt,taget/libvirt,VenkatDatta/libvirt,olafhering/libvirt,libvirt/libvirt,zippy2/libvirt,jfehlig/libvirt,taget/libvirt,crobinso/libvirt,jardasgit/libvirt,zippy2/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,zippy2/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,libvirt/libvirt,datto/libvirt,olafhering/libvirt,jfehlig/libvirt,andreabolognani/libvirt,datto/libvirt,taget/libvirt,jardasgit/libvirt,zippy2/libvirt,eskultety/libvirt,andreabolognani/libvirt,eskultety/libvirt,VenkatDatta/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,jardasgit/libvirt,VenkatDatta/libvirt,taget/libvirt,VenkatDatta/libvirt,datto/libvirt,andreabolognani/libvirt,crobinso/libvirt,jardasgit/libvirt,eskultety/libvirt,taget/libvirt,andreabolognani/libvirt,datto/libvirt,jfehlig/libvirt,eskultety/libvirt,jardasgit/libvirt,eskultety/libvirt,nertpinx/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,olafhering/libvirt,libvirt/libvirt,crobinso/libvirt,datto/libvirt,VenkatDatta/libvirt,nertpinx/libvirt,nertpinx/libvirt,crobinso/libvirt,libvirt/libvirt,jfehlig/libvirt