The patch I4217bd00d8c253db522241885dba2847a26af6df made the
on_shared_storge flag optional in the compute api in Liberty.
This patch removes the corresponding onSharedStorage flag from the
REST API as nova can easily detect this information.
APIImpact
DocImpact
Implements: bp remove-shared-storage-flag-in-evacuate-api
Change-Id: I54bfa1275e188573c1b95d770d89160a86cdf52c