* src/conf/domain_conf.h: Add new member "target" to struct
_virDomainDeviceDriveAddress.
* src/conf/domain_conf.c: Parse and format "target"
* Lots of tests (.xml) in tests/domainsnapshotxml2xmlout,
tests/qemuxml2argvdata, tests/qemuxml2xmloutdata, and
tests/vmx2xmldata/ are modified for newly introduced
attribute "target" for address of "drive" type.
Some tools, such as virt-manager, prefers having the default USB
controller explicit in the XML document. This patch makes sure there
is one. With this patch, it is now possible to switch from USB1 to
USB2 from the release 0.9.1 of virt-manager.
Fix tests to pass with this change.
