Port unit and integration tests to JUnit 5

[tMaxx]

Description

• Switch from JUnit v4 to v5 for majority of unit, and all integration tests (excluded are knotx-adapter-* modules which are already a part of knotx-data-bridge; see Port tests to JUnit 5 knotx-data-bridge#19)
• Clean up unnecessary Maven test dependencies

Travis build will fail until Knotx/knotx-dependencies#6 and Knotx/knotx-junit5#2 are merged.

Some fixes may still be necessary

Motivation and Context

Part of ongoing work to switch to JUnit 5 in whole Knot.x project. See #417 for further references, scope, and motivation.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

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