Default test runner doesn't support 'suspend execution' anymore

[smitterl]

Describe the bug

In older avocado version without specifying the test runner, I could just hit CTRL+Z to suspend and CTRL+Z to resume the test execution. See. https://github.com/avocado-framework/avocado/blob/92lts/avocado/plugins/runner.py#L149

This behavior is important for avocado-vt tests because I with it I can easily inspect the test environment and the VM or other components when they are in a specific state established by the test script. In some cases, the logging or script might not easily reveal al changes that are made to the SUT during the test script execution. It is also a short-cut that enables me to avoid having to run all steps manually.

Steps to reproduce

avocado run ...
Enter "CTRL + Z"

Expected behavior

The test code execution is suspended at the current status. When I hit "CTRL + Z" again the test script execution is resumed.

Current behavior

Nothing, the signal is not handled.

System information (please complete the following information):

• OS: linux
• Avocado version: 103lts
• Avocado installation method: github ?