[hotfix] notifier cache and storage set to undefined

[benoitvidis]

What does this PR do ?

Fix notifier issue introduced by #1311
Kuzzle notifier is instanciated before the services are and notifier.cache and storage properties were set to undefined.

How should this be manually tested?

bash features/run.sh

[codecov]

Codecov Report

Merging #1316 into 1-dev will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           1-dev   #1316   +/-   ##
=====================================
  Coverage   93.8%   93.8%           
=====================================
  Files         98      98           
  Lines       6991    6991           
=====================================
  Hits        6558    6558           
  Misses       433     433

Impacted Files	Coverage Δ
lib/api/core/notifier.js	72.93% <100%> (ø)	⬆️

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[scottinet]

I did run the functional tests, and then I made a few cosmetic changes and I didn't bother re-running the tests... Sorry. 😑