Some new features.

[zylad]

This PR contains:

• cloud.rb uses aws-sdk now, as this is recommended gem for AWS interaction, also it's way easier t debug that right_aws
• added use_iam variable into the config file. Once proper IAM role is assigned to the instance, no keys are actually needed, in such case use_iam can be set to true and keys related variables will be ignored
• added email_use_local_mta variable into the config file. Once set to true, local MTA will be used and no creds have to be stored in the config file
• added log_level variable into config file. This way it's possible to pass @log.level value over the config file.
• added support for software raids. Once /dev/md\d+ is used as mount_point, the list of devices contained in the array will be extracted, post and pre tasks will be executed before and after creating snapshots of all the devices within a specific array. It will also log the info about the array and disks within it.