AB#2046 : Add option to create SSH users for the first coordinator upon initialization (#133)

* Move `file`, `ssh` and `user` packages to internal
* Rename `SSHKey` to `(ssh.)UserKey`
* Rename KeyValue / Publickey to PublicKey
* Rename SSH key file from "debugd" to "ssh-keys"
* Add CreateSSHUsers function to Core
* Call CreateSSHUsers users on first control-plane node, when defined in config

Tests:
* Make StubUserCreator add entries to /etc/passwd
* Add NewLinuxUserManagerFake for unit tests
* Add unit tests & adjust existing ones to changes

internal/deploy/user/linux_user_test.go

@@ -0,0 +1,123 @@
+package user
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"github.com/spf13/afero"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestGetLinuxUser(t *testing.T) {
+	username := "user"
+
+	testCases := map[string]struct {
+		passwdContents string
+		wantErr        bool
+		wantUser       LinuxUser
+	}{
+		"get works": {
+			passwdContents: "user:x:1000:1000:user:/home/user:/bin/bash\n",
+			wantErr:        false,
+			wantUser: LinuxUser{
+				Username: "user",
+				Home:     "/home/user",
+				Uid:      1000,
+				Gid:      1000,
+			},
+		},
+		"user does not exist": {
+			passwdContents: "",
+			wantErr:        true,
+		},
+		"parse fails": {
+			passwdContents: "invalid contents\n",
+			wantErr:        true,
+		},
+		"invalid uid": {
+			passwdContents: "user:x:invalid:1000:user:/home/user:/bin/bash\n",
+			wantErr:        true,
+		},
+		"invalid gid": {
+			passwdContents: "user:x:1000:invalid:user:/home/user:/bin/bash\n",
+			wantErr:        true,
+		},
+	}
+
+	for name, tc := range testCases {
+		t.Run(name, func(t *testing.T) {
+			assert := assert.New(t)
+			require := require.New(t)
+
+			fs := afero.NewMemMapFs()
+			assert.NoError(afero.WriteFile(fs, "/etc/passwd", []byte(tc.passwdContents), 0o755))
+			manager := NewLinuxUserManagerFake(fs)
+			user, err := manager.getLinuxUser(username)
+
+			if tc.wantErr {
+				assert.Error(err)
+				return
+			}
+			require.NoError(err)
+			assert.Equal(tc.wantUser, user)
+		})
+	}
+}
+
+func TestEnsureLinuxUserExists(t *testing.T) {
+	username := "user"
+
+	testCases := map[string]struct {
+		userCreator *StubUserCreator
+		wantErr     bool
+		wantUser    LinuxUser
+	}{
+		"create works": {
+			userCreator: &StubUserCreator{},
+			wantErr:     false,
+			wantUser: LinuxUser{
+				Username: "user",
+				Home:     "/home/user",
+				Uid:      1000,
+				Gid:      1000,
+			},
+		},
+		"create fails": {
+			userCreator: &StubUserCreator{
+				createUserErr: errors.New("create fails"),
+			},
+			wantErr: true,
+		},
+	}
+
+	for name, tc := range testCases {
+		t.Run(name, func(t *testing.T) {
+			assert := assert.New(t)
+			require := require.New(t)
+
+			fs := afero.NewMemMapFs()
+			manager := NewLinuxUserManagerFake(fs)
+			tc.userCreator.fs = fs
+			manager.Creator = tc.userCreator
+			user, err := manager.EnsureLinuxUserExists(context.Background(), username)
+
+			if tc.wantErr {
+				assert.Error(err)
+				return
+			}
+			require.NoError(err)
+			assert.Equal(tc.wantUser, user)
+			assert.ElementsMatch([]string{username}, tc.userCreator.usernames)
+		})
+	}
+}
+
+func TestStringInSlice(t *testing.T) {
+	assert := assert.New(t)
+	testSlice := []string{"abc", "efg", "xyz"}
+
+	assert.True(stringInSlice("efg", testSlice))
+	assert.False(stringInSlice("hij", testSlice))
+}