ipmi: sdr: add one more condition for sdr dimm is not present case

Symptom:
Verify SDR keyword got failed then cause below test cases FAIL.
Test DIMM SDR Info At Power Off | FAIL |
Test DIMM SDR Info At Power On  | FAIL |

Root cause:
According ipmitool sdr elist for dimm result as below:
When dimm0 with real ram on it the result is "Presence Detected" string,
dimm1 and dimm2 without any ram on it the result is empty string.

For example on Olympus: ipmitool sdr elist
dimm0            | 72h | ok  | 32.25 | Presence Detected
dimm1            | 73h | ok  | 32.26 |
dimm2            | 74h | ok  | 32.27 |

However, auto test case keyword "Verify SDR" didn't consider
result is empty string, just only consider result is "Disabled"
string. Thus, cause test case print "Invalid Presence" then test got failed.

Solution:
Add one more condition about result is empty string for sdr dimm is not present

Tested:
Run robot test -v Test_DIMM_SDR_Info_At_Power_Off/On ipmi/test_ipmi_sdr.robot
Test DIMM SDR Info At Power Off | PASS |
Test DIMM SDR Info At Power On  | PASS |

Signed-off-by: Tim Lee <timlee660101@gmail.com>
Change-Id: Ie8c27e94ba80233db3b3858714e5df6f0d2d5b0f
diff --git a/ipmi/test_ipmi_sdr.robot b/ipmi/test_ipmi_sdr.robot
index 5d2f66d..34f357e 100755
--- a/ipmi/test_ipmi_sdr.robot
+++ b/ipmi/test_ipmi_sdr.robot
@@ -256,7 +256,7 @@
     ${component_name}=  Replace String  ${component_name}  /  _
     ${presence_ipmi}=  Get SDR Presence Via IPMI  ${component_name}${SPACE}
 
-    Run Keyword If  '${presence_ipmi}' == 'Disabled'
+    Run Keyword If  '${presence_ipmi}' == 'Disabled' or '${presence_ipmi}' == ''
     ...    Should Be True  ${presence_rest} == ${0} and ${functional_rest} == ${0}
     ...  ELSE IF  '${presence_ipmi}' == 'Presence Detected' or '${presence_ipmi}' == 'Presence detected'
     ...    Should Be True  ${presence_rest} == ${1} and ${functional_rest} == ${1}