bump gomega and gordon
add integration test for drain functionality

The work for this is not yet done.
run-garden-linux: forward args
command runner: don't propagate signals to child

These commands are expected to be unaffected by the server receiving signals,
as the server will intercept TERM/INT to perform a clean shutdown and stop
handling requests. Most requests are handled using the command runner, so
forwarding the signals is counter productive, as the commands are expected to
complete normally.

[#61232150]
implement clean shutdown for server

This adds a .Stop to the server that blocks until in-flight requests are
completed. Unbounded requests like Link, Spawn, and Run are ignored and don't
prevent the server from shutting down.

The executable now traps INT and TERM to perform a clean shutdown.

[#61232150]