Disable auto-reload

Auto-reload seems to cause problems with sqlalchemy MetaData
because it assumes that load order does not make any difference.

This patch disables implecit auto-reload in debug mode and allows
to turn it on using the AUTO_RELOAD configuration parameter.

Developer documention should be updated.

DocImpact
Closes-bug: #1398390
Change-Id: I1fac49eaa519d443e42e0b27c0742cb59dcedad4
Merge "Disable auto-reload"