Add support for stopping/starting ProcessLogHandler from API

tfw/components/process_management/process_log_handler.py

@@ -16,17 +16,20 @@ class ProcessLogHandler:
         self._initial_log_tail = log_tail
 
         self.command_handlers = {
-            'process.log.set': self.handle_set
+            'process.log.set': self.handle_set,
+            'process.log.start': self.handle_start,
+            'process.log.stop': self.handle_stop
         }
 
     def start(self):
-        self._monitor = LogInotifyObserver(
-            connector=self.connector,
-            process_name=self.process_name,
-            supervisor_uri=self._supervisor_uri,
-            log_tail=self._initial_log_tail
-        )
-        self._monitor.start()
+        if not self._monitor:
+            self._monitor = LogInotifyObserver(
+                connector=self.connector,
+                process_name=self.process_name,
+                supervisor_uri=self._supervisor_uri,
+                log_tail=self._initial_log_tail
+            )
+            self._monitor.start()
 
     def handle_event(self, message, _):
         try:
@@ -40,5 +43,16 @@ class ProcessLogHandler:
         if data.get('tail'):
             self._monitor.log_tail = data['tail']
 
+    def handle_start(self, _):
+        self.start()
+
+    def handle_stop(self, _):
+        self._stop_monitor()
+
+    def _stop_monitor(self):
+        if self._monitor:
+            self._monitor.stop()
+            self._monitor = None
+
     def cleanup(self):
-        self._monitor.stop()
+        self._stop_monitor()