ensure_unicode with normalize for py3 compatibility

[gzussa]

What does this PR do?

normalize is being ensure_unicode almost everywhere but not everywhere.
Hence, I am moving the logic as part of the normalize method since it needs to be done all the time.

Motivation

Python 3 compatibility

Additional Notes

Anything else we should know when reviewing?

Review checklist (to be filled by reviewers)

• PR title must be written as a CHANGELOG entry (see why)
• Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• PR must have changelog/ and integration/ labels attached
• Feature or bugfix must have tests
• Git history must be clean
• If PR adds a configuration option, it must be added to the configuration file.

[codecov]

Codecov Report

Merging #3218 into master will increase coverage by 0.52%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #3218      +/-   ##
==========================================
+ Coverage    83.1%   83.62%   +0.52%     
==========================================
  Files         707      700       -7     
  Lines       39356    38667     -689     
  Branches     4684     4613      -71     
==========================================
- Hits        32705    32336     -369     
+ Misses       5254     4973     -281     
+ Partials     1397     1358      -39