minor #14937 Standardize the name of the exception variables (javiereguiluz)

This PR was squashed before being merged into the 2.3 branch (closes #14937).

Discussion
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Standardize the name of the exception variables

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

See symfony/symfony-docs#4491 for the context of this change.

In Symfony source code there are 410 `try ... catch` blocks. More than 95% of them use `$e` as the name of the exception variable. After applying these changes, 407 out of 410 variables are named `$e`.

These are the three cases where I didn't change the name of the `$e` variable:

  * Nested exception in https://github.com/symfony/symfony/blob/2.3/src/Symfony/Component/Routing/Matcher/RedirectableUrlMatcher.php#L40. It uses `$e2` as the name of the nested variable.
  * Nested exception in https://github.com/symfony/symfony/blob/2.3/src/Symfony/Bundle/TwigBundle/TwigEngine.php#L82. I changed the name of the `$ex` variable to `$e2` to match the previous syntax.
  * https://github.com/symfony/symfony/blob/2.3/src/Symfony/Component/Console/Helper/DialogHelper.php#L463. I don't know if it's safe to change the name of the `$error` exception variable.

Commits
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e8b924c Standardize the name of the exception variables

Author: fabpot

DataCollector/RequestDataCollector.php

@@ -125,7 +125,7 @@ public function collect(Request $request, Response $response, \Exception $except
                         'file' => $r->getFileName(),
                         'line' => $r->getStartLine(),
                     );
-                } catch (\ReflectionException $re) {
+                } catch (\ReflectionException $e) {
                     if (is_callable($controller)) {
                         // using __call or  __callStatic
                         $this->data['controller'] = array(

Tests/DependencyInjection/ContainerAwareHttpKernelTest.php

@@ -137,10 +137,10 @@ public function testHandleRestoresThePreviousRequestOnException($type)
         try {
             $kernel->handle($request, $type);
             $this->fail('->handle() suppresses the controller exception');
-        } catch (\PHPUnit_Framework_Exception $exception) {
-            throw $exception;
-        } catch (\Exception $actual) {
-            $this->assertSame($expected, $actual, '->handle() throws the controller exception');
+        } catch (\PHPUnit_Framework_Exception $e) {
+            throw $e;
+        } catch (\Exception $e) {
+            $this->assertSame($expected, $e, '->handle() throws the controller exception');
         }
     }