I added an error check to 'Read Attribute' keyword in lib/rest_client.robot.

Change-Id: Ibba76cef3b3795db4c2f6cebca661ad3bf3b512f
Signed-off-by: Michael Walsh <micwalsh@us.ibm.com>
diff --git a/lib/rest_client.robot b/lib/rest_client.robot
index 425e5dc..1477b05 100644
--- a/lib/rest_client.robot
+++ b/lib/rest_client.robot
@@ -141,6 +141,7 @@
     [Arguments]    ${uri}    ${attr}    ${timeout}=10  ${quiet}=${QUIET}
     ${resp}=  OpenBMC Get Request  ${uri}/attr/${attr}  timeout=${timeout}
     ...  quiet=${quiet}
+    Should Be Equal As Strings  ${resp.status_code}  ${HTTP_OK}
     ${content}=     To Json    ${resp.content}
     [Return]    ${content["data"]}