migrate: bump ghost limit
migrate: bump ghost limit

1MB is not very big, let's make that bigger.

Signed-off-by: Tycho Andersen <10c18fcb898ee6b17d6575d444b125d10b3f4d6a@canonical.com>

akshaykarle/lxd,chrisglass/lxd,stgraber/lxd,hallyn/lxd,ollie314/lxd,atxwebs/lxd,akshaykarle/lxd,ollie314/lxd,Skarlso/lxd,stgraber/lxd,mjeanson/lxd,georghopp/lxd,pcdummy/lxd,georghopp/lxd,erikmack/lxd,hallyn/lxd,akshaykarle/lxd,mjeanson/lxd,Skarlso/lxd,hallyn/lxd,lxc/lxd,chrisglass/lxd,Skarlso/lxd,stgraber/lxd,jsavikko/lxd,atxwebs/lxd,jsavikko/lxd,pcdummy/lxd,erikmack/lxd,techtonik/lxd,stgraber/lxd,stgraber/lxd,lxc/lxd,hallyn/lxd,pcdummy/lxd,jsavikko/lxd,georghopp/lxd,lxc/lxd,stgraber/lxd,lxc/lxd,techtonik/lxd,atxwebs/lxd,lxc/lxd,mjeanson/lxd,atxwebs/lxd,chrisglass/lxd,erikmack/lxd,lxc/lxd,techtonik/lxd,hallyn/lxd,hallyn/lxd,lxc/lxd,ollie314/lxd,Skarlso/lxd,stgraber/lxd