Use Context in ssh client

[guettli]

/kind feature

Currently, the ssh client used by caph does not use the Context.

This means, when the ctx times out, the ssh client does not notice that.

Current code:

type Factory interface {
	NewClient(Input) Client
}

type Input struct {
	IP         string
	PrivateKey string
	Port       int
}

We could add Context to Input.

Using the ctx is not straight forward, because the ssh package was created before context was added to Go.

But it is not difficult either:

1. create conn with net.Dialer.DialContext(ctx, ...)
2. pass that conn into ssh.NewClientConn(...)
3. in a goroutine: select { case <-ctx.Done(): conn.Close() }

Additional benefit: We could get the logger from the context.

---

Alternative:

Currently:

type Client interface {
	GetHostName() Output
	GetHardwareDetailsRAM() Output
	GetHardwareDetailsNics() Output
	...

We add the ctx to each function of the interface:

type Client interface {
	GetHostName(ctx context.Context) Output
...