* Implement notifies for transfer plugin (#3972)

* Fix notifies in transfer plugin
Signed-off-by: Miek Gieben <miek@miek.nl>

* Make it compile
Signed-off-by: Miek Gieben <miek@miek.nl>

* Port more plugins
Signed-off-by: Miek Gieben <miek@miek.nl>

* golint
Signed-off-by: Miek Gieben <miek@miek.nl>

* Fix tests
Signed-off-by: Miek Gieben <miek@miek.nl>

* Fix notifies in transfer plugin
Signed-off-by: Miek Gieben <miek@miek.nl>

* Make it compile
Signed-off-by: Miek Gieben <miek@miek.nl>

* Port more plugins
Signed-off-by: Miek Gieben <miek@miek.nl>

* golint
Signed-off-by: Miek Gieben <miek@miek.nl>

* Fix tests
Signed-off-by: Miek Gieben <miek@miek.nl>

* Fix tests
Signed-off-by: Miek Gieben <miek@miek.nl>

* really fix test
Signed-off-by: Miek Gieben <miek@miek.nl>

* Implement ixfr fallback and unify file and auto for transfering
Signed-off-by: Miek Gieben <miek@miek.nl>

* Add transfer tests

copied and modified from #3452
Signed-off-by: Miek Gieben <miek@miek.nl>

* Test correct selection of plugin
Signed-off-by: Miek Gieben <miek@miek.nl>

* add upstream back in
Signed-off-by: Miek Gieben <miek@miek.nl>

* Implement ixfr fallback and unify file and auto for transfering
Signed-off-by: Miek Gieben <miek@miek.nl>

* fix test
Signed-off-by: Miek Gieben <miek@miek.nl>

* properly merge
Signed-off-by: Miek Gieben <miek@miek.nl>

* Remove plugin/kubernetes/setup_transfer_test.go
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>
Co-authored-by: Miek Gieben <miek@miek.nl>