qemu: Convert boolean flags to enum flags in qemuDomainStorageSourceAccessModify
qemu: Convert boolean flags to enum flags in qemuDomainStorageSourceAccessModify

Upcoming patches will add a few more flags. Add an enum to collect them
so that we don't end up with multiple bools.

Signed-off-by: Peter Krempa <2cf5c04c61aa466e4a47bfedc747d17279c72ffc@redhat.com>
Reviewed-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>

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