Don't lose AttributeError in API Wrappers

Instead of (implicitly) catching the AttributeError, and later
creating and raising a new one, we just re-raise the original
exception. This way all the information from the original is
retained, including the name of the actual object on which it
happened.

Change-Id: Idc0c5a8ed5dfca6a8724e393c220baf9960564ed
Closes-bug: #1274097
Always pass 'modal' context variable to workflow template

Workflow templates rely on 'modal' context variable to be true for
modal dialogs. Still, when rendering from WorkflowView,
this variable is missing. This causes e.g. absent cancel and close
buttons in flavor creating dialog (and also affects Tuskar UI).

Change-Id: I76b1f0b97c14280db7cb880651e663147103438f
Closes-Bug: #1273874
Merge "Don't lose AttributeError in API Wrappers"