Don't swallow missing SR error

[Rick Harris]

Received the following traceback when starting up the compute-worker: http://paste.openstack.org/show/36738/

Root-cause turned out to be a missing SR: the `update_stats` code in xenapi.hosts.py would detect the missing SR, log an error and then bail out before filling in the hypervisor_hostname key.

Since the exception was swallowed, this was more difficult to track down than it had to be.

A better solution would be, since these stats are required, making an SR required, we should *raise* an exception when the SR isn't found.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/27981

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/27981
Committed: http://github.com/openstack/nova/commit/b6aac988e46147154d49e938ecf9b67831613636
Submitter: Jenkins
Branch: master

commit b6aac988e46147154d49e938ecf9b67831613636
Author: Rick Harris <email address hidden>
Date: Wed May 1 21:47:35 2013 +0000

    xenapi: Don't swallow missing SR exception

    The existing code would catch a missing SR exception and bail out of the
    `update_status` method before finishing, causing required keys to be missing.
    The end-result was code breaking later on when it tried to access these keys.

    Since an SR is required to generate these required stats keys, we shouldn't
    swallow the StorageRepositoryNotFound exception and instead should fail-fast.

    Fixes bug 1175357

    Change-Id: I3d65ae807fb2d86277bc0061c1967a87792b6662

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/grizzly
Review: https://review.openstack.org/28075

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/28075
Committed: http://github.com/openstack/nova/commit/498ce526c1c2ce1ad1e17af9fc4a3ff67b0b09a4
Submitter: Jenkins
Branch: stable/grizzly

commit 498ce526c1c2ce1ad1e17af9fc4a3ff67b0b09a4
Author: Rick Harris <email address hidden>
Date: Wed May 1 21:47:35 2013 +0000

    xenapi: Don't swallow missing SR exception

    The existing code would catch a missing SR exception and bail out of the
    `update_status` method before finishing, causing required keys to be missing.
    The end-result was code breaking later on when it tried to access these keys.

    Since an SR is required to generate these required stats keys, we shouldn't
    swallow the StorageRepositoryNotFound exception and instead should fail-fast.

    Fixes bug 1175357

    Change-Id: I3d65ae807fb2d86277bc0061c1967a87792b6662
    (cherry picked from commit b6aac988e46147154d49e938ecf9b67831613636)