Remove default value for ssl_certificate_arn

[tnation14]

Overview

This PR removes the default value for ssl_certificate_arn (which is now outdated) from variables.tf, and updates scripts/infra to use a .tfvars file to make it easier to override other defaults in the future. Also, bump ECS WebService module version to 0.4.0 and make some small fixes to the build pipeline.

Changes

• Remove default value for ssl_certficate_arn. That value is now provided to terraform via a tfvars file.
• Add docker-compose.ci.override.yml for local deployments.
• Add --no-include-email flag to ECR login command
• Bump ECS WebService module to 0.4.0.

Fixes #94 See azavea/operations#202

Testing

• I deployed this PR from Travis. Build logs are here.
• Run scripts/infra according to the instructions in the new deployment README, ensure no changes are necessary.

  $ export GT_TRANSIT_SETTINGS_BUCKET=geotrellis-site-production-config-us-east-1
  $ export AWS_PROFILE=geotrellis
  $ export TRAVIS_COMMIT=$(git rev-parse --short master)
  $ docker-compose -f docker-compose.ci.yml run --rm terraform ./scripts/infra plan