Improve for-each-server script

[mitchb]

See RT ticket ​960054

The attached script was contributed by Pete Kruskall (tek)

[mitchb]

Pete Kruskall's exec.py script

[adehnert]

Is this actually better than the for-each-server currently in the locker? Glancing briefly at exec.py, it looks like it:

• Improperly handles quoting (or, perhaps, "more improperly", given that I gather that ssh will screw up the quoting anyway)
• Improperly sets a username if the command you run on the server includes a -u argument (like, say, pgrep or pkill)

I'm not sure that there's actually anything in that script we want to use.

[adehnert]

ETIMEOUT

"Improve for-each-server" isn't really an actionable ticket, and zephyr, Trac, and RT appear not to have disputed my claim that "there's [not] actually anything in that script we want to use".