improve missing arg handling

- better error messages
- missing instrument is only allowed with 'list'
- missing argument to be replaced with ? in error message
- sea cli may now be given with 'graph' or 'sea' for service

seaman.py

@@ -68,7 +68,7 @@ class SeaManager(ServiceManager):
 %(legend)s
     """
 
-    def do_cli(self, ins):
+    def do_cli(self, ins, service=None):
         if self.wildcard(ins):
             raise UsageError('wildcards not allowed in sea cli')
         try:
@@ -78,7 +78,8 @@ class SeaManager(ServiceManager):
             print(str(e))
         except KeyError:  # running on an other machine?
             self.do_help()
-        run_command('six -sea %s' % ins, wait=True)
+        service = service or 'sea'
+        run_command(f'six -{service} {ins}', wait=True)
 
     def do_gui(self, ins='', *args):
         if ins and self.wildcard(ins):
@@ -196,6 +197,8 @@ class SeaManager(ServiceManager):
                     argdict['ins'] = arg
                 else:
                     raise UsageError('unknown argument: %s' % arg)
+            else:
+                print('env variable "InstrumentHostList" is not defined')
         result = [argdict.pop('ins', '')]
         service = argdict.pop('service', '')
         if service: