Allow profile start time equals end time

As we are using the last sample time as end time, there is chance we
have the start time equals to end time.

Author: Colman Yau

codeguru_profiler_agent/model/profile.py

@@ -43,9 +43,9 @@ def end(self):
     @end.setter
     def end(self, value):
         self._validate_positive_number(value)
-        if value <= self.start:
+        if value < self.start:
             raise ValueError(
-                "Profile end value must be bigger than {}, got {}".format(self.start, value))
+                "Profile end value must be greater than or equals to {}, got {}".format(self.start, value))
         self._end = value
         # this is the total cpu time spent in this application since start, not just the overhead
         self.cpu_time_seconds = time.process_time() - self._start_process_time