123046 jvonka: Update API tests for - tweaks for common code, also check that Last-Modified and Expires are not null when downloading file content/rendition
RA-641, RA-676, RA-829, RA-830
git-svn-id: https://svn.alfresco.com/repos/alfresco-enterprise/alfresco/HEAD/root@126523 c4b6b30b-aa2e-2d43-bbcb-ca4b014f7261