Fixed random failure cases of IPMI user

For example: Pairs of cases
"Test IPMI Administrator Privilege Level" and "Test IPMI No Access Privilege Level".
"Test IPMI User Privilege Level" and "Enable IPMI User And Verify".
Once their user id are the same, the latter may fail.

To resolve this, delete the user that each case has just created to
ensure that it won't affect other following cases.

Signed-off-by: Tony Lee <tony.lee@quantatw.com>
Change-Id: Iae41bf0e69d6efc392c1e59e48dff565a9efd179
diff --git a/lib/ipmi_client.robot b/lib/ipmi_client.robot
index 4484f61..b97beab 100755
--- a/lib/ipmi_client.robot
+++ b/lib/ipmi_client.robot
@@ -376,7 +376,7 @@
     # username    The user name (e.g. "root", "robert", etc.).
     # password    The user password (e.g. "0penBmc", "0penBmc1", etc.).
 
-    ${output}=  Run External IPMI Standard Command
+    ${output}=  Wait Until Keyword Succeeds  15 sec  5 sec  Run External IPMI Standard Command
     ...  sel info  U=${username}  P=${password}
     Should Contain  ${output}  SEL Information  msg=SEL information not present