libxl: fix timer configuration
libxl: fix timer configuration

The current logic around configuring timers in libxl based on
virDomainDef object is a bit brain dead. Unsupported timers are
silently ignored and tsc is only recognized if it is the first
timer specified.

Change the logic to reject unsupported timers and honor the tsc
timer regardless of its order when multiple timers are specified.

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