QEMUD_CMD_FLAG_PCI_MULTIBUS should be set in the function
qemuCapsExtractVersionInfo()

The flag QEMUD_CMD_FLAG_PCI_MULTIBUS is used in the function
qemuBuildDeviceAddressStr(). All callers get qemuCmdFlags
by the function qemuCapsExtractVersionInfo() except that
testCompareXMLToArgvFiles() in qemuxml2argvtest.c.

So we should set QEMUD_CMD_FLAG_PCI_MULTIBUS in the function
qemuCapsExtractVersionInfo() instead of qemuBuildCommandLine()
because the function qemuBuildCommandLine() does not be called
when we attach a pci device.

tests: set QEMUD_CMD_FLAG_PCI_MULTIBUS in testCompareXMLToArgvFiles()

set QEMUD_CMD_FLAG_PCI_MULTIBUS before calling qemuBuildCommandLine()
as the flags is not set by qemuCapsExtractVersionInfo().
Signed-off-by: NWen Congyang <wency@cn.fujitsu.com>