Add missing changelogs

Author: ocelotl

Diff for: ext/opentelemetry-ext-django/CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+
+- Update environment variable names, prefix changed from `OPENTELEMETRY` to `OTEL` ([#904](https://github.com/open-telemetry/opentelemetry-python/pull/904))
 - Use one general exclude list instead of two ([#872](https://github.com/open-telemetry/opentelemetry-python/pull/872))
 
 ## 0.8b0

Diff for: ext/opentelemetry-ext-elasticsearch/CHANGELOG.md

@@ -2,8 +2,10 @@
 
 ## Unreleased
 
+- Update environment variable names, prefix changed from `OPENTELEMETRY` to `OTEL` ([#904](https://github.com/open-telemetry/opentelemetry-python/pull/904))
+
 ## Version 0.10b0
 
 Released 2020-06-23
 
-- Initial release
+- Initial release

Diff for: ext/opentelemetry-ext-flask/CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+- Update environment variable names, prefix changed from `OPENTELEMETRY` to `OTEL` ([#904](https://github.com/open-telemetry/opentelemetry-python/pull/904))
 - Use one general exclude list instead of two ([#872](https://github.com/open-telemetry/opentelemetry-python/pull/872))
 
 ## 0.7b1

Diff for: ext/opentelemetry-ext-pyramid/CHANGELOG.md

@@ -2,10 +2,11 @@
 
 ## Unreleased
 
+- Update environment variable names, prefix changed from `OPENTELEMETRY` to `OTEL` ([#904](https://github.com/open-telemetry/opentelemetry-python/pull/904))
 - Use one general exclude list instead of two ([#872](https://github.com/open-telemetry/opentelemetry-python/pull/872))
 
 ## 0.9b0
 
 Released 2020-06-10
 
-- Initial release
+- Initial release

Diff for: opentelemetry-sdk/CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+- Update environment variable names, prefix changed from `OPENTELEMETRY` to `OTEL`
+  ([#904](https://github.com/open-telemetry/opentelemetry-python/pull/904))
 - Add support for resources and resource detector
   ([#853](https://github.com/open-telemetry/opentelemetry-python/pull/853))
 - Rename record_error to record_exception