Update hypervisor_hostname after live migration

After a live migration, the OS-EXT-SRV-ATTR:hypervisor_hostname
attribute of the instance is not updated correctly.  This change
adds a parameter to the call to _instance_update that fixes the
problem.

Fixes bug 1173376

Change-Id: I40f1ead2d93c7a9979a914e0fb96e3e5bb287b48
(cherry picked from commit 8c8e44cf37be9c6a9f418e923c9ff16df8619832)
Don't raise unnecessary stack traces in EC2 API

exception.EC2APIError exceptions are always expected, so no reason to have a
LOG.exception when one is raised.  Furthermore nova.api.ec2.ec2_error already
logs the exception so the duplicate log statement is just removed

Fix Bug 1180973

Change-Id: I4b42a9a764f6e15bb94a383e8a725d52d7436bd7
(cherry picked from commit dc887267572c821ce97bec9536a699b72bdae443)
Merge "Update hypervisor_hostname after live migration" into stable/grizzly
Merge "Don't raise unnecessary stack traces in EC2 API" into stable/grizzly