conf: Refactor formatting of startupPolicy in virDomainDiskSourceFormatInternal
conf: Refactor formatting of startupPolicy in virDomainDiskSourceFormatInternal

Move it to a single location which also allows to get rid of the
temporrary variable.

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

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