Make releases for all packages with user-visible feature / bugfixes

[tseaver]

Release needed:

• core-0.25.0 (PR Prep core-0.25.0 release. #3526)
• datastore-1.1.0 (PR Prep datastore-1.1.0 release. #3527)
• logging-1.1.0 (PR Prep logging-1.1.0 release. #3528)
• storage-1.2.0 (exclude "requester pays") (PR Prep storage-1.2.0 release. #3529) (PR Prep storage-1.2.0 release. #3540)
• bigquery-0.25.0 (PR Prep bigquery-0.25.0 release. #3530)
• pubsub-0.26.0 (PR Prep pubsub-0.26.0 release. #3532)
• bigtable-0.25.0 (PR Prep bigtable-0.25.0 release. #3534)
• language-0.25.0 (PR Prep language-0.25.0 release. #3535)
• vision-0.25.0 (PR Prep vision-0.25.0 release. #3537)

No release needed, exception for "release the world" to pick up new google-cloud-core:

• dns-0.25.0 (PR Prep dns-0.25.0 release. #3541)
• error_reporting-0.25.0 (PR Prep error-reporting-0.25.0 release. #3542)
• monitoring-0.25.0 (PR Prep monitoring-0.25.0 release. #3543)
• resource_manager-0.25.0 (PR Prep resource-manager-0.25.0 release. #3544)
• runtimeconfig-0.25.0 (PR Prep runtimeconfig-0.25.0 release. #3545)
• spanner-0.25.0 (PR Prep spanner-0.25.0 release. #3536)
• speech-0.26.0 (PR Prep speech-0.26.0 release. #3546)
• translate-0.25.0 (PR Prep translate-0.25.0 release. #3547)

No release needed at all:

• videointelligence does not depend on google-cloud-core.

Finally:

• Umbrella release (PR Prep umbrella 0.26.0 release. #3549)

[tseaver]

See:

https://github.com/GoogleCloudPlatform/google-cloud-python/releases/tag/0.26.0