Glance: Fix typo in notifier-strategy

The 'notifier-strategy' parameter in glance-api.conf was
misspelt, as a result it wasn't getting set properly.

Change-Id: I2703421d22dfec9ea344da765c3f8551bfd39bad
Provide an override level for os-apply-config

This allows elements to override the templates provided by other
elements using templates in post-os-apply-config. For example, the
logstash element provides a very basic logstash.conf. This change allows
another element to easily substitute a more useful version.

README.md has been rewritten as it was fairly sparse to begin with.

Change-Id: I14a103bf16554dc42b9c8ba1d4fefcacf6f07786
Allow tempest tenant isolation

Defines TEMPEST_ALLOW_TENANT_ISOLATION env variable to control
tempest tenant isolation. True by default as testr runs with
the --parallel option.

Change-Id: I60c39f6055a31311af2f573b997757a761ec6121
Merge "Glance: Fix typo in notifier-strategy"
Merge "Allow tempest tenant isolation"
Merge "Provide an override level for os-apply-config"