Fix how QUnit.newMwEnvironment merges live and custom settings

We shouldn't merge a live state's setting value with a custom
value anymore as it has been done since I7d20f0b2f4. Doing this
can produce very unpredictable outcome of tests depending on the
server's state and will prevent from being able to properly
define a test's conditions.

Change-Id: I7ad058a45708244918211658b5d4e07f69abba31
Merge "Fix how QUnit.newMwEnvironment merges live and custom settings"