Fix crash in dashboard: mimetype has been removed
Fix crash in dashboard: mimetype has been removed

mimetype parameter has been renamed to content_type in Django 1.5, and removed
in 1.7

Change-Id: Iae4a34a7a37841767c03c08d308f8b3b1d9ed63e
(cherry picked from commit 326a7249087388128c36a40d18563098e847df9f)

Linaro/lava-server,Linaro/lava-server,Linaro/lava-server,Linaro/lava-server