This one is a relatively easy move.  We don't ever convert the
enum to or from strings (it is inferred from other elements in
the xml, rather than directly represented).

* src/conf/domain_conf.h (virDomainDiskSecretType): Move...
* src/util/virstoragefile.h (virStorageSecreteType): ...and
rename.
* src/conf/domain_conf.c (virDomainDiskSecretType): Drop unused
enum conversion.
(virDomainDiskAuthClear, virDomainDiskDefParseXML)
(virDomainDiskDefFormat): Adjust clients.
* src/qemu/qemu_command.c (qemuGetSecretString): Likewise.
* src/qemu/qemu_conf.c (qemuTranslateDiskSourcePoolAuth):
Likewise.
Signed-off-by: NEric Blake <eblake@redhat.com>