conf: Don't require 'def' in virDomainDiskDefParse
conf: Don't require 'def' in virDomainDiskDefParse

In some use cases (mostly in tests) it is not required to check the
seclabel definition validity. Add possibility to call
virDomainDiskDefParse without the domain definition.

Signed-off-by: Peter Krempa <2cf5c04c61aa466e4a47bfedc747d17279c72ffc@redhat.com>

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