catch InstanceUserDataTooLarge when create instance at api layer

[jichenjc]

we should catch InstanceUserDataTooLarge when we create an instance
because compute/api.py might report this exception

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/105095

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/105095
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=fa7da67af1ee1c71900224efaa68bafa309b1def
Submitter: Jenkins
Branch: master

commit fa7da67af1ee1c71900224efaa68bafa309b1def
Author: jichenjc <email address hidden>
Date: Thu Jul 3 09:37:09 2014 +0800

    Handle InstanceUserDataTooLarge at api layer

    compute layer might raise InstanceUserDataTooLarge exception,
    this patch catches the exception at API layer and handle it.

    Closes-Bug: #1338473

    Change-Id: I881e526eaa51ab28316f643430d904f620123d56