[plugins] make pem certificate regexp stricter

This was changed in de5fd69
with no explanations, revert to the previous stricter regexp,
so we can apply do_*_private_sub() without fearing false positive.

sos/report/plugins/__init__.py

@@ -64,7 +64,7 @@ def _node_type(st):
     return ''
 
 
-_certmatch = re.compile("-*BEGIN.*?-*END", re.DOTALL)
+_certmatch = re.compile("-----BEGIN.*?-----END", re.DOTALL)
 _cert_replace = "-----SCRUBBED"