[dockerhub] Fix docker image builder

[alexandrebouthinon]

What does this PR do ?

Use script to build docker images only on *-dev branches. For master branch and releases, use automated build on dockerhub

Finally, this PR will fix the bash script used to build kuzzle images.

How should this be manually tested?

Check Travis file

[codecov-io]

Codecov Report

Merging #1216 into 1-dev will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##            1-dev    #1216   +/-   ##
=======================================
  Coverage   93.88%   93.88%           
=======================================
  Files          95       95           
  Lines        6555     6555           
=======================================
  Hits         6154     6154           
  Misses        401      401

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[Aschen]

Are you sure ? Dockerhub does not handle multistage build, so how it can build our production images ?
We are supposed to build 2 images with a single Dockerfile: kuzzleio/kuzzle and kuzzleio/plugin-dev