improve the way we terminate subprocess during test runs

[GustavoCaso]

Some of our test we are leaving lingering processes after completing.

• Using the t.Context when using runCliCommand sometimes failed to execute the command because of the context being cancelled. This was particular hapenning on our Cleanup function for our server.
• The other test that left lingering process was TestRunCommand_Foreground . Looks like our tests creates a many processes: go test, go run . so when sending the SIGTERM to go run . command we still have a process left after the test.
  We fixed by creating a process group associated with the go run . command, so all sub processes created can be terminated using syscall.Kill(-cmd.Process.Pid, syscall.SIGTERM)