Issue minishift#317 Refactoring existing hostfolder code and implemen…

…ting sshfs hostfolders

- Add hidden sftpd command
- Refactor existing hostfolder actions
- Introducing hostfolder.Manager as entry point for hostfolder operations
- Introducing HostFolder interface as common abstraction for any host folder type
- Split impl details between CIFS and SSHFS
- Allow to configure host folder interactively as well as non-interactively (Issue minishift#959)
- Adding docs

Gopkg.toml

@@ -174,3 +174,8 @@ ignored = ["github.com/Sirupsen/logrus"]
 [[constraint]]
   name = "github.com/stretchr/testify"
   version = "=v1.2.0"
+
+[[constraint]]
+  name = "github.com/pkg/sftp"
+  version = "1.0.0"
+

cmd/minishift/cmd/config/config.go

@@ -95,6 +95,7 @@ var (
 	// Host Folders
 	HostFoldersMountPath = createConfigSetting("hostfolders-mountpath", SetString, nil, nil, true, nil)
 	HostFoldersAutoMount = createConfigSetting("hostfolders-automount", SetBool, nil, nil, true, nil)
+	HostFoldersSftpPort  = createConfigSetting("hostfolders-sftp-port", SetInt, []setFn{validations.IsPositive}, nil, true, nil)
 
 	// Image caching
 	ImageCaching = createConfigSetting("image-caching", SetBool, nil, nil, true, true)