This patch adds error-handling to the user guide document for cases
where the v2 APIs 'instantiate', 'scale' and 'heal' fail due to lack of
availability zone resources.
If StandardUserData is used as UserData class, it is possible to
reselect the availability zone as error-handling.
Implements: blueprint enhance-placement
Change-Id: Ib0065e2f7c085583d53abf14a6be07e8e77f81ff