Migrate softlayer sdk from IBM-Cloud/softlayer-go-sdk to softlayer/softlayer-go-sdk (offically supported)

[hkantare]

In IBM Cloud Terraform provider we customized the officially supported https://github.com/softlayer/softlayer-go to adopt some features for Terraform and Softlayer. Published the SDK https://github.com/IBM-Cloud/softlayer-go/tree/terraform

softlayer/softlayer-go@master...IBM-Cloud:softlayer-go:terraform

• Add support for refresh token in softlayer-go
• Add ClusterIdentifier and HostId attributes for terraform
• Add ReservedCapacityId attributes for terraform

[allmightyspiff]

Opened a pull request: softlayer/softlayer-go#195
I reverted the datatype changes, but IAM stuff looks ok. I need to get the build to pass, and will likely add some unit tests around this code, but otherwise it looks like a good addition.