Fix endless loop with log clear attempt in redfish

Some redfish implementations endlessly mutate
their etag.  This makes it impossible to
fully establish atomicity.

Move the logic as much server side as possible.
There is still a window where entries change
between fetching the entries and the loginfo,
but there is little hope.

Change-Id: I9135b96acf82f06bc8622efb4d53d0bc695d1758

pyghmi/redfish/command.py

@@ -1515,18 +1515,19 @@ class Command(object):
                 clearurl = newloginfo.get('Actions', {}).get(
                     '#LogService.ClearLog', {}).get('target', '')
                 while clearurl:
-                    while logtag != newloginfo.get('@odata.etag', None):
-                        logtag = newloginfo.get('@odata.etag', None)
-                        entries = self._do_web_request(entriesurl, cache=False)
-                        newloginfo = self._do_web_request(lurl, cache=False)
                     try:
                         self._do_web_request(clearurl, method='POST',
-                                             etag=logtag)
+                                             etag=logtag, payload={})
                         clearurl = False
                     except exc.PyghmiException as e:
                         if 'EtagPreconditionalFailed' not in str(e):
                             raise
+                        # This doesn't guarantee atomicity, but it mitigates
+                        # greatly.  Unfortunately some implementations
+                        # mutate the tag endlessly and we have no hope
+                        entries = self._do_web_request(entriesurl, cache=False)
                         newloginfo = self._do_web_request(lurl, cache=False)
+                        logtag = newloginfo.get('@odata.etag', None)
             for log in entries.get('Members', []):
                 record = {}
                 record['log_id'] = logid