Resolve problems with the optional use of 'start_cmd'

[thomas]

Bee's optional start_cmd causes a considerable amount of distracting noise in pull requests.

My proposal is to phase the command out by turning it into a 'noop', and later on remove it completely.

[pmenzel]

Having the executed command listed on the command line (in lieu of set -x) is very handy, so please keep it.