Added AWS_DISABLE_CONFIG_AUTO_DISCOVERY constant to config file

Config auto discovery caused open_basedir restriction on Cloudfoundry servers (AppFog). I added the AWS_DISABLE_CONFIG_AUTO_DISCOVERY constant to the kohana config file.

Here's the error:

ErrorException: file_exists(): open_basedir restriction in effect. File(/home/vcap-user-###/.aws/sdk/config.inc.php) is not within the allowed path(s): (/usr/share/php:/usr/share/pear:/usr/share/php/libzend-framework-php:/var/vcap.local/dea/apps/###/tmp:/var/vcap.local/dea/apps/###/app)
1
File "/mnt/var/vcap.local/dea/apps/###/app/modules/storage/vendor/aws-sdk/sdk.class.php" line 1511 in error_handler