mbedtls-amis.yaml: Add timestamp wrapper

Signed-off-by: Arthur She <arthur.she@linaro.org>
Change-Id: Ic2add6fb937e6614233b0eedeaeac933d8a779e9
diff --git a/mbedtls-amis.yaml b/mbedtls-amis.yaml
index a83cc4d..0f9a660 100644
--- a/mbedtls-amis.yaml
+++ b/mbedtls-amis.yaml
@@ -14,6 +14,8 @@
     node: build-amd64-private
     concurrent: false
     display-name: 'build AMIs for mbedtls'
+    wrappers:
+        - timestamps
     parameters:
     - bool:
         name: BUILD_UBUNTU_AMI