"kpm restore --quiet" hides HTTP requests/cache information

parent #577 

An interesting usage mentioned by @davidfowl  is `kpm --verbose restore --quiet`. For my implementation, in this case, `--verbose` wins and here is the reason:
If `--quiet` wins, `kpm restore` blocks without showing HTTP requests/cache information. So the user might not notice that he mistakenly specified `--verbose` and `--quiet` together because he might think that `kpm restore` is blocking for some silent operations.
If `--verbose` wins, we show a bunch of HTTP request/cache information instantly after the user hit Enter key. So the user can easily notice he specified `--verbose`. The basic idea is that we make the behavior obvious & quick enough to draw users' attention.

@Eilon , do you like the idea above? Or we can give an error saying `--verbose` and `--quiet` are mutually exclusive.

Please first have a look at the value assignment of `Reports.Verbose` here: https://github.com/aspnet/KRuntime/blob/kpm-quiet-option-hides-http-requests-during-restore/src/Microsoft.Framework.PackageManager/Program.cs#L76

Let's assume `--quiet` is specified, then there are two possible cases:
1. `--verbose` is not specified, then `Reports.Verbose` points to a `NullReport` object, which swallows `WriteLine()` operation and do nothing else. So it is quiet.
2. `--verbose` is specified, then `Reports.Verbose` points to the same `IReport` object as `Reports.Information`, which prints to console. So `--verbose` wins.