feat: create tunnel inside NewSession (#286)

* feat: create tunnel inside NewSession

We want to create the tunnel when we create the session. This change
allows us to nicely ignore the problem of creating a tunnel when we
already have a proxy, as well as the problem of locking. Everything is
happening, in fact, inside of the NewSession factory.

Modify miniooni such that --tunnel is just syntactic sugar for
--proxy, at least for now. We want, in the future, to teach the
tunnel to possibly use a socks5 proxy.

Because starting a tunnel is a slow operation, we need a context in
NewSession. This causes a bunch of places to change. Not really a big
deal except we need to propagate the changes.

Make sure that the mobile code can create a new session using a
proxy for all the APIs we support.

Make sure all tests are still green and we don't loose coverage of
the various ways in which this code could be used.

This change is part of https://github.com/ooni/probe/issues/985.

* changes after merge

* fix: only keep tests that can hopefully work

While there, identify other places where we should add more
tests or fix integration tests.

Part of https://github.com/ooni/probe/issues/985

cmd/ooniprobe/internal/ooni/ooni.go

@@ -1,6 +1,7 @@
 package ooni
 
 import (
+	"context"
 	_ "embed" // because we embed a file
 	"io/ioutil"
 	"os"
@@ -26,7 +27,7 @@ type ProbeCLI interface {
 	IsBatch() bool
 	Home() string
 	TempDir() string
-	NewProbeEngine() (ProbeEngine, error)
+	NewProbeEngine(ctx context.Context) (ProbeEngine, error)
 }
 
 // ProbeEngine is an instance of the OONI Probe engine.
@@ -201,7 +202,7 @@ func (p *Probe) Init(softwareName, softwareVersion string) error {
 // NewSession creates a new ooni/probe-engine session using the
 // current configuration inside the context. The caller must close
 // the session when done using it, by calling sess.Close().
-func (p *Probe) NewSession() (*engine.Session, error) {
+func (p *Probe) NewSession(ctx context.Context) (*engine.Session, error) {
 	kvstore, err := engine.NewFileSystemKVStore(
 		utils.EngineDir(p.home),
 	)
@@ -211,7 +212,7 @@ func (p *Probe) NewSession() (*engine.Session, error) {
 	if err := os.MkdirAll(utils.TunnelDir(p.home), 0700); err != nil {
 		return nil, errors.Wrap(err, "creating tunnel dir")
 	}
-	return engine.NewSession(engine.SessionConfig{
+	return engine.NewSession(ctx, engine.SessionConfig{
 		KVStore:         kvstore,
 		Logger:          enginex.Logger,
 		SoftwareName:    p.softwareName,
@@ -222,8 +223,8 @@ func (p *Probe) NewSession() (*engine.Session, error) {
 }
 
 // NewProbeEngine creates a new ProbeEngine instance.
-func (p *Probe) NewProbeEngine() (ProbeEngine, error) {
-	sess, err := p.NewSession()
+func (p *Probe) NewProbeEngine(ctx context.Context) (ProbeEngine, error) {
+	sess, err := p.NewSession(ctx)
 	if err != nil {
 		return nil, err
 	}