buildstep: fix updateSummary race condition

Stop trigger integration tests, revelead a race
condition. When updateSummary is called
before the step is started, self.stepid is not set
and thus the setStepStateString(self.stepid, ...)
call failed.

This commit fixes that issue.

Change-Id: I725b9a4f791b1063bdac892be9dca27471f4b452
Signed-off-by: Ion Alberdi <ialberdi@intel.com>

master/buildbot/process/buildstep.py

@@ -319,7 +319,7 @@ def __init__(self, **kwargs):
         self.statistics = {}
         self.logs = {}
         self._running = False
-
+        self.stepid = None
         self._start_unhandled_deferreds = None
 
     def __new__(klass, *args, **kwargs):
@@ -415,8 +415,9 @@ def methodInfo(m):
         if not isinstance(stepResult, unicode):
             raise TypeError("step result string must be unicode (got %r)"
                             % (stepResult,))
-        yield self.master.data.updates.setStepStateString(self.stepid,
-                                                          stepResult)
+        if self.stepid is not None:
+            yield self.master.data.updates.setStepStateString(self.stepid,
+                                                              stepResult)
 
         if not self._running:
             buildResult = summary.get('build', None)