storage: Refactor storage pool type checks
storage: Refactor storage pool type checks

Refactor the code for both startPool (*Mount) and stopPool (*Unmount) code
paths by introducing virStorageBackendFileSystemIsValid.

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