ppms driver now uses command handlers

this is a simplicifcation for the ppms driver

- the derivation of a changecmd from a querycmd is moved to
  CmdHandler.__init__
- the special treatment of handlers when writing configured
  parameters has moved to CmdHandler.write
- introduced Drivable.isDriving, changed Module.isBusy

Change-Id: I8862ecda9c8cc998bb018bd960f31c9488146707
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/22033
Tested-by: JenkinsCodeReview <bjoern_pedersen@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

secop_psi/ls370res.py

@@ -36,6 +36,13 @@ class CmdHandler(secop.commandhandler.CmdHandler):
     CMDARGS = ['channel']
     CMDSEPARATOR = ';'
 
+    def __init__(self, name, querycmd, replyfmt):
+        changecmd = querycmd.replace('?', ' ')
+        if not querycmd.endswith('?'):
+            changecmd += ','
+        super().__init__(name, querycmd, replyfmt, changecmd)
+
+
 rdgrng = CmdHandler('rdgrng', 'RDGRNG?%(channel)d', '%d,%d,%d,%d,%d')
 inset = CmdHandler('inset', 'INSET?%(channel)d', '%d,%d,%d,%d,%d')
 filterhdl = CmdHandler('filt', 'FILTER?%(channel)d', '%d,%d,%d')