When mgt sends a command to the cache process, whether it is a period
ping or an actual operation, it must complete within cli_timeout. When
the cache fails to meet this requirement, mgt sends a SIGQUIT signal
to the cache process. As a result the cache process MAY dump a core
file for post-mortem analysis.

When the core file is missing we are left to our own devices.

To mitigate this, a new signal handler is added for SIGQUIT, but since
we can't (or don't even try to) guarantee delivery on the CLI thread,
we make a last-ditch effort to forward SIGQUIT signals to properly
panic from the CLI thread. With a regular panic we may get both a panic
report and a core dump.

I didn't add test coverage for this, since we try to avoid intentional
core dumps in test cases with the `no_coredump` feature flag that turns
SIGQUIT into a SIGKILL signal.