Let QA_REMOTE_GRID be nil or empty string

What does this MR do?

In its current implementation, if ENV['QA_REMOTE_GRID'] is empty string "", remote_grid will produce http://:80

The guard clause will return if ENV['QA_REMOTE_GRID'] is nil or empty string.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer