Fixes/resolve command node in assert commands

[gravityvi]

Changes

• Delay the resolution of assert node so that command node (child node of assert resolves first).
• Added test to check if async/await custom commands using asserts works fine.
• fix static assertions (assert.ok) to return a promise in case of async node.
• reject assert node if error is assertion assertion error.
• fix a test to drop status params from promise result.

Impacts

• fixes #3301