Create at-requires mechanism for containers

Some tests are incompatible with containers, hard to execute in container environment, requiring special additional setup.

The reasons could be:
  - special host or OS configuration setup is required
  - huge disk space or other unusual resource requirements
  - special host/port configuration
  - access to external hosts

Proposal:
  - create a new at-requires definition/method and implement it
  - the name could be 'containerized'
  - annotate the incompatible tests with "@requires !containerized"