explicitly report missing dependencies in the environment, e.g. `nc`

[jiridanek]

I observed failure

INFO[0000] repo.Repository.Run, [rev-parse --show-toplevel]  sourceLine="repo/repo.go:63"
INFO[0000] repo.Repository.Run complete. Err: <nil>      sourceLine="repo/repo.go:72"
INFO[0000] git.NewRepository: /tmp/scoot-tmp-024806936/gitdb-repo-963465879, top: /tmp/scoot-tmp-024806936/gitdb-repo-963465879  sourceLine="repo/repo.go:132"
INFO[0010] Killing 1 cmds                                sourceLine="setup/cmds.go:75"
INFO[0010] SIGINT: 32304 /root/go/bin/apiserver          sourceLine="setup/cmds.go:91"
INFO[0010] Cmd 32304 (/root/go/bin/apiserver) finished   sourceLine="setup/cmds.go:149"
INFO[0010] All completed                                 sourceLine="setup/cmds.go:100"
FATA[0010] port 11100 is not up after 5s                 sourceLine="setup-cloud-scoot/main.go:53"
exit status 1

Looking at the code, it became apparent I am missing nc. I installed that and it fixed the problem.

scoot/scheduler/setup/ports.go

Lines 24 to 30 in 9b02ac8

	// Use exec.Command because we don't worry about these getting orphaned,
	// and don't want to fill up our Cmds's list of running cmds
	cmd := exec.Command("nc", "-z", "localhost", strconv.Itoa(port))
	if err := cmd.Run(); err == nil {
	log.Infof("Port %v active", port)
	return nil
	}

# yum install -y nc

In the future, there should be better error message. Possibly a check for all binaries up front? Possibly avoid using external nc, since go has reasonable facilities for network programing in the std lib.