Backend enhancements for transformation plan request to better support UI

[bzwei]

Small enhancements to transformation plan request

1. Treat ServiceTemplateTransformationPlanRequest as backend only so that it does not show on the service requests screen
2. Set the request's description the same as plan's name. The migration UI shows the request by description. The description can link to the plan.

[bzwei]

@miq-bot add_label transformation, enhancement
@miq-bot assign @gmcculloug
@tinaafitz @mkanoor @lfu please review

[tinaafitz]

@bzwei Looks good.

[bzwei]

I followed the example in parent class' implementation

[miq-bot]

Checked commits bzwei/manageiq@fbfaeec~...ba8d622 with ruby 2.3.3, rubocop 0.52.0, haml-lint 0.20.0, and yamllint 1.10.0
3 files checked, 1 offense detected

app/models/miq_request.rb

• ❗ - Line 102, Col 32 - Style/MutableConstant - Freeze mutable objects assigned to constants.

[simaishi]

Gaprindashvili backport details:

$ git log -1
commit dc902b6565e3e64a2b34c72150275c5f059b3b47
Author: Greg McCullough <gmccullo@redhat.com>
Date:   Mon Mar 5 10:28:15 2018 -0500

    Merge pull request #17071 from bzwei/v2v_request_desc
    
    Backend enhancements for transformation plan request to better support UI
    (cherry picked from commit b253433b46c24bcc6056eafb24610ed78e55989b)