frappyman: inherit PYTHONPATH from starting process

on SINQ instruments, when frappy is started from nicos,
nicos.conf contains PYTHONPATH  = /home/<instr>:/home/<instr>/.local...
this should be applied to the frappy process too

frappyman.py

@@ -76,6 +76,13 @@ class FrappyManager(ServiceManager):
         cfgpaths = self.config_dirs(ins, service)
         if cfgpaths:
             env['FRAPPY_CONFDIR'] = os.pathsep.join(cfgpaths)
+        # merge PYTHONPATH from servicemanager.cfg with the one from environment
+        pypathlist = []
+        for pypath in env.get('PYTHONPATH'), os.environ.get('PYTHONPATH'):
+            if pypath is not None:
+                pypathlist.extend(p for p in pypath.split(':') if p not in pypathlist)
+        if pypathlist:
+            env['PYTHONPATH'] = os.environ['PYTHONPATH'] = ':'.join(pypathlist)
         return start_dir, env
 
     def do_start(self, ins, service=None, cfg='', restart=False, wait=False, logger=None):