Convert terraform related global variables to a dictionary

[jimright]

After reviewing the Terraform variables with @wmudge, we agreed that changing the Terraform global variables to be a dictionary gives a better structure to the inputs. Changes done in conjunction with cloudera.exe PR#100

An example of the Terraform-related entries in the Cloudera-Deploy definition file following this change are shown below.

# Deployment engine
infra_deployment_engine: terraform

# Terraform Options
terraform:
  state_storage: remote_s3
  auto_remote_state: True
  remote_state_bucket: example-state-bucket-config
  remote_state_lock_table: example-state-lock-table-config

Signed-off-by: Jim Enright [email protected]