Rename DriveInfo.onerror to on_write_error

Either rename variables and functions to refer to write errors (which is what
they actually do) or introduce a parameter to distinguish reads and writes.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

vl.c

@@ -1964,6 +1964,10 @@ BlockInterfaceErrorAction drive_get_on_error(
 {
     DriveInfo *dinfo;
 
+    if (is_read) {
+        return BLOCK_ERR_REPORT;
+    }
+
     QTAILQ_FOREACH(dinfo, &drives, next) {
         if (dinfo->bdrv == bdrv)
             return is_read ? dinfo->on_read_error : dinfo->on_write_error;