[Test] Fix stale element error in messaging integration test

[ltrung]

Issue #:
The messaging session integration test sometimes failed with stale element error in the last step when checking whether we no longer see the disconnect button because there can be a race condition when the page refreshes right after Selenium webdriver found the element reference causing it to be stale and isDisplayed will throw StaleElementReferenceError.

Description of changes:

• Moving the 1st wait time up first before the check to give some buffer between connect/disconnect step and the check.
• Add try/catch just to be safe.
• Refactor the test.

Testing:

Can these tested using a demo application? Please provide reproducible step-by-step instructions.
N/A

Checklist:

1. Have you successfully run npm run build:release locally? N/A

2. Do you add, modify, or delete public API definitions? If yes, has that been reviewed and approved? N/A

3. Do you change the wire protocol, e.g. the request method? If yes, has that been reviewed and approved? N/A

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.