qemu: Escape commas for qemuBuildSCSIiSCSIHostdevDrvStr
    
    Add comma escaping for netsource. This is done here because
    qemuBuildNetworkDriveStr has other external callers which
    may not expect an escaped comma; however, this particular
    command building path needs to perform the escaping for the
    hostdev command line, so we do it now to ensure src->path
    and src->host->name are covered.
    
    Signed-off-by: Anya Harter <aharter@redhat.com>