monitor: Remove bootstrap file on failure only

As bootstrapMonitor is run many times and each execution takes taime it's
better to have the status file there during monitor is running, especially if
previous runs were good.

This file is used by other tools to check last state of bootstrap monitor, and
if it disappears for execution of monitor it can result with false alarms.

/reviewed-on !70

slapos/monitor/monitor.py

@@ -354,9 +354,6 @@ class Monitoring(object):
 
   def bootstrapMonitor(self):
 
-    if os.path.exists(self.promise_output_file):
-      os.unlink(self.promise_output_file)
-
     # save pid of current process into file
     with open(self.pid_file, 'w') as pid_file:
       pid_file.write(str(os.getpid()))
@@ -378,6 +375,9 @@ class Monitoring(object):
       with open(self.promise_output_file, 'w') as promise_file:
         promise_file.write("")
       print("SUCCESS: bootstrap is OK")
+    elif os.path.exists(self.promise_output_file):
+      os.unlink(self.promise_output_file)
+
 
     return 0