populate --context delemap: fix default wait argument

See https://forum.image.sc/t/omero-metadata-fails-on-deletemap-when-well-to-images-was-set-yes/27761 and #11 (comment)

The default wait value of the CLI command is set -1 but the logic for handling indefinite waiting is not implemented in the plugin:

omero-metadata/src/omero_metadata/cli.py

Lines 481 to 484 in ad50292

    
           wait = args.wait 
        
           if wait: 
        
               ms = 5000 
        
               loops = int((wait * 1000) / ms) + 1

This means the default populate --context deletemap command will fail immediately unless --wait is overriden.

Looking at the implementation in the base GraphControl, two options can be considered for the immediate fix:

change the default wait value to None and use some sensible default values for loops and ms
implement the wait=-1 use case i.e. wait for the deletion command to finish by default and allow it to be aborted via the CLI

	wait = args.wait
	if wait:
	ms = 5000
	loops = int((wait * 1000) / ms) + 1