Handle SIGTERM on Linux

[alnlarsen]

OpenTAP currently handles SIGINT by aborting the root TapThread context. This is great for a graceful shutdown, as any plugin can register cleanup hooks in their context.

However, SIGINT is typically limited to keyboard interrupts (e.g. CTRL-C) unless specifically sent. On Linux systems, a graceful shutdown is typically requested with the SIGTERM signal. This is the case for e.g. Kubernetes where OpenTAP is often deployed.

I propose assigning SIGTERM to the same hook as SIGINT is currently assigned, such that a pod receiving a SIGTERM signal gets the same behavior as typing CTRL-C in a terminal.

[github-actions]

A fix for this is in OpenTAP version 9.22.0-beta.8+bedfc82f or later.

[sebastian-pop]

Implemented. Verified on 9.22.0-rc.2