Move ExtractFile from hyperkit to drivers

So that it can be used in other drivers too

pkg/drivers/hyperkit/driver.go

@@ -427,7 +427,7 @@ func (d *Driver) extractKernel(isoPath string) error {
 		{"/boot/initrd", "initrd"},
 	} {
 		fullDestPath := d.ResolveStorePath(f.destPath)
-		if err := ExtractFile(isoPath, f.pathInIso, fullDestPath); err != nil {
+		if err := pkgdrivers.ExtractFile(isoPath, f.pathInIso, fullDestPath); err != nil {
 			return err
 		}
 	}

pkg/drivers/iso.go

@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-package hyperkit
+package drivers
 
 import (
 	"fmt"

pkg/drivers/iso_test.go

@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-package hyperkit
+package drivers
 
 import (
 	"testing"