Enforce sprintf for exceptions

| Q             | A
| ------------- | ---
| Bug fix?      |no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | [yes|no]
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | https://github.com/symfony/symfony-docs/pull/2483

Changed format of exceptions which concatenate strings as follows

````
throw new \Exception('The '.$something.' needs the '.$foobar.' parameter');
````

to

````
throw new \Exception(sprintf('The %s needs the %s parameter', $something, $foobar));
````

This follows discussion on mailing list: https://groups.google.com/forum/?fromgroups#!topic/symfony-devs/tecj3UOAueM

Unit test results are pending...