commands: Make commands.Execute return a Response object

We have no global `Hugo` object no more (yay!), and there are some external tools that depends on that value.

These tools need to use get that value from `Response.Result`.

Note that `commands.Execute` now also takes the arguments as a string slice. This should also make it easier to use, not having to modify `os.Args`.

This commit also wraps up this particular issue. Phew!

Test coverage in /commands before: 14.4%
Now:  53.5%

Still work to do, now it is at least possible.

Closes #4598

commands/commands_test.go

@@ -23,6 +23,24 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+func TestExecute(t *testing.T) {
+
+	assert := require.New(t)
+
+	dir, err := createSimpleTestSite(t)
+	assert.NoError(err)
+
+	defer func() {
+		os.RemoveAll(dir)
+	}()
+
+	resp := Execute([]string{"-s=" + dir})
+	assert.NoError(resp.Err)
+	result := resp.Result
+	assert.True(len(result.Sites) == 1)
+	assert.True(len(result.Sites[0].RegularPages) == 1)
+}
+
 func TestCommands(t *testing.T) {
 
 	assert := require.New(t)
@@ -72,7 +90,7 @@ func TestCommands(t *testing.T) {
 
 	for _, test := range tests {
 
-		hugoCmd := newHugoCompleteCmd()
+		hugoCmd := newHugoCompleteCmd().getCommand()
 		test.flags = append(test.flags, "--quiet")
 		hugoCmd.SetArgs(append(test.commands, test.flags...))