Add support for creating bare metal hosts on SoftLayer

[hashibot]

This issue was originally opened by @ErikEvenson as hashicorp/terraform#8326. It was migrated here as part of the provider split. The original body of the issue is below.

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Overview: http://www.softlayer.com/bare-metal-servers

API: https://sldn.softlayer.com/blog/bpotter/ordering-bare-metal-servers-using-softlayer-api

[albee-jhoney]

Refer to the IBM Cloud provider here: https://github.com/IBM-Cloud/terraform-provider-ibm for support for bare-metal-servers; docs - https://ibm-cloud.github.io/tf-ibm-docs/