Fix an error of checking reboot type (sonic-net#14155)

What is the motivation for this PR?
There is another reboot cause Unknown (First boot of SONiC version xxx) on kvm besides User issued xxx' command, which will cause error 'NoneType' object has no attribute 'groups' based on the current code. To address this, this PR suggests a conditional check to ensure that the match object is not None before attempting to access its 'groups' attribute, thereby preventing such issue.

How did you do it?
This PR suggests a conditional check to ensure that the match object is not None before attempting to access its 'groups' attribute, thereby preventing such issue.

How did you verify/test it?

Author: yutongzhang-microsoft

tests/common/reboot.py

@@ -344,7 +344,9 @@ def get_reboot_cause(dut):
     # is such like "User issued 'xxx' command [User: admin, Time: Sun Aug  4 06:43:19 PM UTC 2024]"
     # So, use the above pattern to get real reboot cause
     if dut.facts["asic_type"] == "vs":
-        cause = re.search("User issued '(.*)' command", cause).groups()[0]
+        match = re.search("User issued '(.*)' command", cause)
+        if match:
+            cause = match.groups()[0]
 
     for type, ctrl in list(reboot_ctrl_dict.items()):
         if re.search(ctrl['cause'], cause):