Currently, when running specs, the output of rake tasks is spamming
the tests results.
This PR configures Rake so that it runs in quiet mode during specs. This
disables the internal messages of rake during tests.
However our own `puts` also need to be conditionned to the verbosity of
rake. Using a simple `rake_puts` helper allows the info messages to be
displayed when running the rake task manually, but not during tests.
Before:
```
$ bin/rspec spec/lib/rake
Randomized with seed 6544
1 Mails::ClosedMail to clean
cleaning Mails::ClosedMail #1
1 Mails::InitiatedMail to clean
cleaning Mails::InitiatedMail #1
1 Mails::ReceivedMail to clean
cleaning Mails::ReceivedMail #1
1 Mails::RefusedMail to clean
cleaning Mails::RefusedMail #1
1 Mails::WithoutContinuationMail to clean
cleaning Mails::WithoutContinuationMail #1
.....Champ 0/1
.Champ 0/1
.
```
After:
```
$ bin/rspec spec/lib/rake
Randomized with seed 6544
.......
```
