refactor: move more commands to internal/cmd (#207)

* refactor: move more commands to internal/cmd

Part of https://github.com/ooni/probe/issues/1335.

We would like all commands to be at the same level of engine
rather than inside engine (now that we can do it).

* fix: update .gitignore

* refactor: also move jafar outside engine

* We should be good now?

internal/engine/shellx/shellx_test.go

@@ -0,0 +1,44 @@
+package shellx
+
+import "testing"
+
+func TestRun(t *testing.T) {
+	if err := Run("whoami"); err != nil {
+		t.Fatal(err)
+	}
+	if err := Run("./nonexistent/command"); err == nil {
+		t.Fatal("expected an error here")
+	}
+}
+
+func TestRunQuiet(t *testing.T) {
+	if err := RunQuiet("true"); err != nil {
+		t.Fatal(err)
+	}
+	if err := RunQuiet("./nonexistent/command"); err == nil {
+		t.Fatal("expected an error here")
+	}
+}
+
+func TestRunCommandline(t *testing.T) {
+	t.Run("when the command does not parse", func(t *testing.T) {
+		if err := RunCommandline(`"foobar`); err == nil {
+			t.Fatal("expected an error here")
+		}
+	})
+	t.Run("when we have no arguments", func(t *testing.T) {
+		if err := RunCommandline(""); err == nil {
+			t.Fatal("expected an error here")
+		}
+	})
+	t.Run("when we have a single argument", func(t *testing.T) {
+		if err := RunCommandline("ls"); err != nil {
+			t.Fatal(err)
+		}
+	})
+	t.Run("when we have more than one argument", func(t *testing.T) {
+		if err := RunCommandline("ls ."); err != nil {
+			t.Fatal(err)
+		}
+	})
+}