Handle the lava-health check inside an atomic check

Queries in exception handlers in migrations need to
isolate the query to ensure a correct rollback.

Change-Id: Id34b5ba44933cd2b33a3bd193d5efb80e2f37b71
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
Improve again the release script

The script now accepts one optional parameter (--changelog/-c) that will
generate the changelog, ordered by commit time.
Only the first line of the commit message will be printed.

Change-Id: Id1af42148f2d24090ee126577518432c83778a7e
Allows to select the branch to compare with master

Change-Id: I16d14705e4e19c6842efc9295a01fa7c44597f36