Don't inherit from base.html in 500 error page

For server errors, the context passed to the template is empty,
so things like STATIC_URL and context processors don't work.

Fixes bug 1067206 for the folsom branch.

This has been adapted to folsom release and is a backport from master.

Change-Id: I5cd60523360d71b088226e4d0f87d88bac8a8df3
Avoid cinder calls, when cinder is unavailable

When a volume service is not available, then a cinder client can not
be created. This patch skips the calls, so that dashboard doesn't
break any more.

This is a backport to Folsom release, as this turned out to be a major
issue.
Fixes bug 1084137

Change-Id: I8f2f8b0b131b4bb5319d74f6da48671f146d7e00
Merge "Avoid cinder calls, when cinder is unavailable" into stable/folsom
Merge "Don't inherit from base.html in 500 error page" into stable/folsom