Bug 989137 - Part 11: Make service initialization and uninitialization more robust; r=gfritzsche

Subsequent patches were running into race conditions and bugs related to
Experiments instance initialization state. This patch plugs the
necessary holes in initialization state management to unblock work.

The fixes are far from robust. There are still race conditions and bugs.
They should probably be addressed later.

--HG--
extra : rebase_source : 5f0c7fa1f554d09a21b1452506884dc771cb829d