conf: use disk source accessors in qemu/

conf: use disk source accessors in qemu/

Part of a series of cleanups to use new accessor methods.

* src/qemu/qemu_conf.c (qemuCheckSharedDevice)
(qemuAddSharedDevice, qemuRemoveSharedDevice, qemuSetUnprivSGIO):
Use accessors.
* src/qemu/qemu_domain.c (qemuDomainDeviceDefPostParse)
(qemuDomainObjCheckDiskTaint, qemuDomainSnapshotForEachQcow2Raw)
(qemuDomainCheckRemoveOptionalDisk, qemuDomainCheckDiskPresence)
(qemuDiskChainCheckBroken, qemuDomainDetermineDiskChain):
Likewise.
* src/qemu/qemu_hotplug.c (qemuDomainChangeEjectableMedia)
(qemuDomainCheckEjectableMedia)
(qemuDomainAttachVirtioDiskDevice, qemuDomainAttachSCSIDisk)
(qemuDomainAttachUSBMassstorageDevice)
(qemuDomainAttachDeviceDiskLive, qemuDomainRemoveDiskDevice)
(qemuDomainDetachVirtioDiskDevice, qemuDomainDetachDiskDevice):
Likewise.
* src/qemu/qemu_migration.c (qemuMigrationStartNBDServer)
(qemuMigrationDriveMirror, qemuMigrationCancelDriveMirror)
(qemuMigrationIsSafe): Likewise.
* src/qemu/qemu_process.c (qemuProcessGetVolumeQcowPassphrase)
(qemuProcessHandleIOError, qemuProcessHandleBlockJob)
(qemuProcessInitPasswords): Likewise.
* src/qemu/qemu_driver.c (qemuDomainChangeDiskMediaLive)
(qemuDomainGetBlockInfo, qemuDiskPathToAlias): Likewise.

Signed-off-by: Eric Blake <eblake@redhat.com>