Upgrade to Vault 0.11.1

[lawliet89]

• Use Vault Agent for AWS Auth
• Test out AWS secrets engine configuration with the changes in the AWS secrets engine changes ([WIP] Update aws_secret_backend_role with changes from Vault 0.11 hashicorp/terraform-provider-vault#194)

[lawliet89]

#171 Bumps to 0.11.

Working on updating the Vault Terraform provider to fix the second issue in the list above in hashicorp/terraform-provider-vault#194