1115499: Allow enable/disable repos in same command.

Combining was previously possible, but all enable options were processed
before disable, meaning --disable "*" --enable "a" would end up with "a" disabled.

Uses an optparse callback to process CLI arguments and store an ordered list
of tuples of enable/disable + repoid.

Assumes the user wants them processed in the order they appear on the command
line, the last match will be the one that wins for a particular repo.
Could probably simplify this method with something like
```python
vars(parser.values).setdefault('repo_actions', []).append((opt[2:], value))
```

This seems like a candidate for a named tuple, but meh.  Instead of storing enable/disable, it could make sense to store either a boolean (enabled, ex: opt.endswith('enable')), or the new status '0'/'1' (if we're parsing it a bit here, we might as well take it all the way to the final parsed value).  Not sure we'd gain much though

This might be more readable if we rename "value" to "repoid"