Adjust test suite to take into account that MAT does not clean PDF files anymore

During 2.7 release cycle, Mat has been upgraded to 0.5.2-3+deb8u1, which removes PDF support.

We have a scenario testing Mat with this kind of file in our test suite, so we need to adapt it. I guess switching to some image containing EXIF metadata would be much more stable.

Feature Branch: test/11901-mat-does-not-clean-PDF-anymore

Parent Task: #10288

Original created by @bertagaz on 11901 (Redmine)

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