MAGETWO-32612: magento composer uninstall not removing module

- added magento-composer-installer to the root package.
This is workaround and it will be removed after bug composer/composer#3791 will be fixed.

Conflicts:
	composer.lock

Author: Ivan Gavryshko

app/etc/vendor_path.php

@@ -7,4 +7,4 @@
 /**
  * Path to Composer vendor directory
  */
-return 'vendor';
+return './vendor';

composer.json

@@ -32,7 +32,8 @@
         "magento/zendframework1": "1.12.10",
         "composer/composer": "1.0.0-alpha8",
         "monolog/monolog": "1.11.0",
-        "tubalmartin/cssmin": "2.4.8-p4"
+        "tubalmartin/cssmin": "2.4.8-p4",
+        "magento/magento-composer-installer": "*"
     },
     "require-dev": {
         "phpunit/phpunit": "4.1.0",