Fix bug: incompatible jobs with explicit placement.

[Lifann]

Description

Brief Description of the PR: In graph mode, when the device context is explicitly specified by device or replica_device_setter, the session may raise incompatible error if the devices cannot be merged. This PR fixed the case.

Type of change

• Bug fix
• New Tutorial
• Updated or additional documentation
• Additional Testing
• New Feature

Checklist:

• I've properly formatted my code according to the guidelines
  • By running yapf
  • By running clang-format
• This PR addresses an already submitted issue for TensorFlow Recommenders-Addons
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works

How Has This Been Tested?

If you're adding a bugfix or new feature please describe the tests that you ran to verify your changes:

• demo

[rhdong]

LGTM