do not request a pty

post-processor/atlas: adjust test for cross-platform filepath separator

Make TestLongestCommonPrefix cross-platform friendly by defining
the test cases with filepath.Separator.

Fixes test failure on Windows.

Fix config interpolation for some builders

OpenStack uses official OpenStack client

documentation: subnet_id is required for non-default VPC

* b-amazon-error-on-ssh-error:
  builder/amazon: Properly return error code on ssh errors