Allow --restart-times to specify rule name to be applied to

[kpj]

For example, jobs which download data via the internet can sometimes (unexpectedly) crash due to network problems. In such cases, restarting them is the only possible fix.

Snakemake has the parameter --restart-times N which restarts any failing job N times.
It would be great if this parameter would optionally take a rule name to only allow multiple restarts for that particular rule.

It is certainly possible to handle automatic retries within the rule itself, but using Snakemake's --restart-times parameter seems like a more elegant way of handling this (in particular with snakemake wrappers).

[kpj]

This is now reasonably solved by #1649.