Bug 837001 - Disable remote debugging by default. r=fabrice

Marionette requires that remote debugging be disabled, so this changes
remote debugging to be off by default.
Merge pull request #7932 from dhylands/dhylands-837001

Bug 837001 - Disable remote debugging by default. r=fabrice

This goes along with bug 836973 which has landed on m-c, b2g18 and v1.0.0