generalconfig: streamlined config discovery

determine generalconfig file location in order:
  - command line argument
  - environment variable
  - git location (../cfg)
  - local location (cwd)
  - global location (/etc/frappy)

Change-Id: Ie34bcbd5188837075ee7bb7d5029d676ae72378e
Reviewed-on: https://forge.frm2.tum.de/review/c/secop/frappy/+/34839
Reviewed-by: Bjoern Pedersen <bjoern.pedersen@frm2.tum.de>
Reviewed-by: Alexander Zaft <a.zaft@fz-juelich.de>
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>

bin/frappy-server

@@ -35,7 +35,15 @@ from frappy.server import Server
 
 
 def parseArgv(argv):
-    parser = argparse.ArgumentParser(description="Manage a SECoP server")
+    parser = argparse.ArgumentParser(
+        description="Manage a SECoP server",
+        epilog="""The server needs some configuration, by default from the
+            generalConfig.cfg file. the keys confdir, logdir and piddir have to
+            be set.
+            Alternatively, one can set the environment variables FRAPPY_CONFDIR
+            FRAPPY_LOGDIR and FRAPPY_PIDDIR to set the required values.
+        """
+    )
     loggroup = parser.add_mutually_exclusive_group()
     loggroup.add_argument("-v", "--verbose",
                           help="Output lots of diagnostic information",