Rebase to 5.7.2

Merge pull request #22 from rescale/rebase-softlayer-07-22-2019

Rebase softlayer to upstream - 07 22 2019

v5.5.1

Dedicatedhost#Cancel: cli bug with --immediate flag

We found weird behavior with cancellation if we set `--immediate default=True` in decorator.

`slcli dedicatedhost cancel ID`   => will create immediate cancellation ticket
`slcli dedicatedhost cancel ID --immediate` => will create non-immediate cancellation ticket
Have no idea what is the root cause, fix is to enforce `immediate = True` in function body.