admin: Fix error when server is created

When a server is in building state, any check for actions will throw
faults.BuildInProgress. Catch this exception and do not show actions for
this server.

Fix apyrgio/synnefo#193
admin: Limit allowed_actions in json view

Hide actions that may be allowed for an item but not permitted for a
user.
Merge branch 'feature-admin-actions' into feature-admin