fix(build): add an argument for build prod when it is a Test CI. Adapt travis.yml to use it

[SuperITMan]

ISSUES CLOSED: #572 #566

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/NationalBankBelgium/stark/blob/master/CONTRIBUTING.md#-commit-message-guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[X] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: #572 # 566

What is the new behavior?

Travis build for each PR is faster

Does this PR introduce a breaking change?

[ ] Yes
[X] No

[coveralls]

Coverage decreased (-0.01%) to 92.747% when pulling b954903 on SuperITMan:bugfix/travis-fix-build-time into 771a9b4 on NationalBankBelgium:master.