Ignore stdout/stderr messages before "yum history list"

Yum stderr logs as "Warning: RPMDB modified outside of yum."
are appended to the SSH output which completely breaks the history parsing.
To solve this problem, we need to skip all log lines before transactions.

Signed-off-by: Ronan Abhamon <ronan.abhamon@vates.fr>

lib/host.py

@@ -272,10 +272,19 @@ def get_last_yum_history_tid(self):
             history_str = self.ssh(['yum', 'history', 'list', '--noplugins'])
 
         history = history_str.splitlines()
+        line_index = None
+        for i in range(len(history)):
+            if history[i].startswith('--------'):
+                line_index = i
+                break
+
+        if line_index is None:
+            raise Exception('Unable to get yum transactions')
+
         try:
-            return int(history[2].split()[0])
+            return int(history[line_index + 1].split()[0])
         except ValueError:
-            raise Exception('Unable to parse correctly last yum history tid. Output\n:' + history_str)
+            raise Exception('Unable to parse correctly last yum history tid. Output:\n' + history_str)
 
     def yum_install(self, packages, enablerepo=None):
         logging.info('Install packages: %s on host %s' % (' '.join(packages), self))