Trying to fix drush installation.

Dockerfile

@@ -27,12 +27,11 @@ RUN DEBIAN_FRONTEND=noninteractive apt-get -y install wget git mysql-client mysq
 RUN pear channel-discover pear.phpmd.org && pear channel-discover 'pear.pdepend.org' && pear install --alldeps 'phpmd/PHP_PMD'
 RUN wget https://phar.phpunit.de/phpcpd.phar && chmod +x phpcpd.phar && mv phpcpd.phar /usr/local/bin/phpcpd
 RUN pecl install -Z uploadprogress && echo "extension=uploadprogress.so" >> /etc/php5/apache2/conf.d/uploadprogress.ini && ln -s /etc/php5/mods-available/uploadprogress.ini /etc/php5/apache2/conf.d/20-uploadprogress.ini
-RUN curl -sS https://getcomposer.org/installer | php && mv composer.phar /usr/local/bin/composer && mkdir /opt/drupalextension/
+RUN curl -sS https://getcomposer.org/installer | php && mv composer.phar /usr/local/bin/composer
 COPY composer.json /opt/drupalextension/composer.json
-RUN cd /opt/drupalextension/ && composer install && ln -s /opt/drupalextension/bin/behat /usr/local/bin/behat
-RUN composer global require drush/drush:7.x && composer global update
-RUN drush dl site_audit registre_rebuild -y
-RUN cd /root/.drush && git clone https://github.com/sfl-drupal/po-import.git && drush cc drush
+RUN mkdir /opt/drupalextension/ && cd /opt/drupalextension/ && composer install && ln -s /opt/drupalextension/bin/behat /usr/local/bin/behat
+RUN mkdir /opt/drush/ && composer require drush/drush:7.x && ln -s /opt/drush/bin/drush /usr/local/bin/drush && /usr/local/bin/drush dl site_audit registry_rebuild -y
+RUN cd /root/.drush && git clone https://github.com/sfl-drupal/po-import.git && /usr/local/bin/drush cc drush
 
 # Make mysql listen on the outside
 RUN sed -i "s/^bind-address/#bind-address/" /etc/mysql/my.cnf