Pin python-pymysql latest version MOS repo.

Change-Id: Ia42b38284331484df7bafe80773b7f5e1b28fd01
diff --git a/ironic/api/single.yml b/ironic/api/single.yml
index 0800579..ed73e90 100644
--- a/ironic/api/single.yml
+++ b/ironic/api/single.yml
@@ -1,6 +1,12 @@
 classes:
 - service.ironic.api.single
 parameters:
+  linux:
+    system:
+      package:
+        python-pymysql:
+          fromrepo: ${_param:openstack_version}
+          version: latest
   ironic:
     api:
       bind: