Re-arrange test configurations

[Paul-Ferrell]

Currently tests are organized into a single tests directory, and their source is generally expected to be in the test_src. This makes keeping source and tests organized as a single unit difficult.

Re-organize tests/test_src such that:

• test_src and tests are optional (and no longer created when setting up config areas.
• Suite configs in tests/ at the top level still work as per-current mechanisms, but are deprecated.
• A new suites directory is created by default instead.
  • Suites can exist as just a <suite_name>.yaml, but such suites should not have any locally provided source (downloads are fine though).
  • Suites are expected to be in a directory that determines the suite name.
  • A suite.yamlfile should exist in each directory that contains the Pavilion config for that suite.
  • Source paths are relative to the suite's directory.
  • The . source path should copy the suite directory (except the suite.yaml file, which shouldn't count towards the build hash).