Re: [libvirt] [PATCHv2 8/9] conf: fix omission of <driver> in domain dumpxml

I noticed that depending on the <driver> attributes the user passed in, the output may omit the <driver> element altogether. For example, the rerror_policy has had this problem since commit 4bb4109 in Oct 2011. But in adding testsuite coverage to expose it, I found another problem: the C code is just fine without a driver name, but the XML validator required either a name or a cache mode. * src/conf/domain_conf.c (virDomainDiskDefFormat): Update conditional. * docs/schemas/domaincommon.rng (diskDriver): Simplify. * tests/qemuxml2argvdata/qemuxml2argv-disk-drive-copy-on-read.xml: * tests/qemuxml2argvdata/qemuxml2argv-disk-drive-copy-on-read.args: New files. * tests/qemuxml2argvdata/qemuxml2argv-disk-drive-discard.xml: Enhance test. * tests/qemuxml2xmloutdata/qemuxml2xmlout-disk-drive-discard.xml: Likewise. * tests/qemuxml2argvtest.c (mymain): New test. * tests/qemuxml2xmltest.c (mymain): Likewise.