Initially I wrote the test to cover
f7d6f3e4 (svtools: survive swapout/in of
graphic with embedded pdf, 2016-06-28), but as it turns out the actual
swapin/out code is in vcl, so extend that as well to support pdf data.

Change-Id: I320ea729dce9440b84a5089607807322ea7b0b04
Reviewed-on: https://gerrit.libreoffice.org/26755Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>