Create validation for Sod's shock tube in 3D

[yungyuc]

• create test case to validate the Sod's shock tube in 3D: add a new test file in ftests/gasplus
• include the functional tests as part of the CI test.

[yungyuc]

Originally the issue was titled create unit tests for 3D Sod tube example and had items:

• create unit test(s) to validate the incomplete driven script provided by issue find 3D Sod tube example and play around with it. #112
• include these unit tests as part of the CI test.

It is changed to fit real development plan.

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Originally reported by: Taihsiang Ho (BitBucket: tai271828, GitHub: tai271828)

• Bitbucket: https://bitbucket.org/solvcon/solvcon/issue/127