libmachine: use fmt.Errorf and errors.Wrap instead of custom errors

Error type are not checked or used anywhere else.
The text in ErrHostDoesNotExist is also never displayed as we have an
other check before this one in client.Exist():
`Machine 'crc' does not exist. Use 'crc start' to create it`

pkg/libmachine/host/host.go

@@ -2,11 +2,12 @@ package host
 
 import (
 	"errors"
+	"fmt"
 	"net/rpc"
 	"regexp"
+	"strings"
 
 	log "github.com/code-ready/crc/pkg/crc/logging"
-	"github.com/code-ready/crc/pkg/libmachine/mcnerror"
 	"github.com/code-ready/crc/pkg/libmachine/mcnutils"
 	"github.com/code-ready/machine/libmachine/drivers"
 	"github.com/code-ready/machine/libmachine/state"
@@ -35,10 +36,7 @@ func ValidateHostName(name string) bool {
 
 func (h *Host) runActionForState(action func() error, desiredState state.State) error {
 	if drivers.MachineInState(h.Driver, desiredState)() {
-		return mcnerror.ErrHostAlreadyInState{
-			Name:  h.Name,
-			State: desiredState,
-		}
+		return fmt.Errorf("machine %q is already %s", h.Name, strings.ToLower(desiredState.String()))
 	}
 
 	if err := action(); err != nil {

pkg/libmachine/libmachine.go

@@ -8,13 +8,13 @@ import (
 	log "github.com/code-ready/crc/pkg/crc/logging"
 	"github.com/code-ready/crc/pkg/drivers/hyperv"
 	"github.com/code-ready/crc/pkg/libmachine/host"
-	"github.com/code-ready/crc/pkg/libmachine/mcnerror"
 	"github.com/code-ready/crc/pkg/libmachine/mcnutils"
 	"github.com/code-ready/crc/pkg/libmachine/persist"
 	"github.com/code-ready/crc/pkg/libmachine/version"
 	"github.com/code-ready/machine/libmachine/drivers"
 	rpcdriver "github.com/code-ready/machine/libmachine/drivers/rpc"
 	"github.com/code-ready/machine/libmachine/state"
+	"github.com/pkg/errors"
 )
 
 type API interface {
@@ -91,9 +91,7 @@ func (api *Client) Create(h *host.Host) error {
 	log.Info("Running pre-create checks...")
 
 	if err := h.Driver.PreCreateCheck(); err != nil {
-		return mcnerror.ErrDuringPreCreate{
-			Cause: err,
-		}
+		return errors.Wrap(err, "error with pre-create check")
 	}
 
 	if err := api.Save(h); err != nil {

pkg/libmachine/persist/filestore.go

@@ -9,7 +9,6 @@ import (
 
 	log "github.com/code-ready/crc/pkg/crc/logging"
 	"github.com/code-ready/crc/pkg/libmachine/host"
-	"github.com/code-ready/crc/pkg/libmachine/mcnerror"
 )
 
 type Filestore struct {
@@ -104,9 +103,7 @@ func (s Filestore) Load(name string) (*host.Host, error) {
 	hostPath := filepath.Join(s.GetMachinesDir(), name)
 
 	if _, err := os.Stat(hostPath); os.IsNotExist(err) {
-		return nil, mcnerror.ErrHostDoesNotExist{
-			Name: name,
-		}
+		return nil, fmt.Errorf("machine %s does not exist", name)
 	}
 	data, err := ioutil.ReadFile(filepath.Join(s.GetMachinesDir(), name, "config.json"))
 	if err != nil {