Makefile: refactor environment check
Makefile: refactor environment check

Refactor how and when we check environment setup:
* don't check while populating variables (dev/ci/staging/prod)
* check instead before each action that requires correct env. setup
* also check if you are working on correct AWS account
* because environment script now goes to AWS to retrieve some credentials,
  it will be always necessary to have correct AWS creds configured. As it
  turns out, all the actions in Makefile that required DEPLOY_ENV either did
  some AWS manipulation later, or script that require AWS manipulation did
  call environment.sh, which required DEPLOY_ENV. Thus combine the checks
  into one environment check.

alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf