Add fixtures build tag to all fixtures.go files

Ensure testing dependencies from fixtures don't leak into builds.
diff --git a/openstack/orchestration/v1/buildinfo/fixtures.go b/openstack/orchestration/v1/buildinfo/fixtures.go
index 20ea09b..d1240b8 100644
--- a/openstack/orchestration/v1/buildinfo/fixtures.go
+++ b/openstack/orchestration/v1/buildinfo/fixtures.go
@@ -1,3 +1,5 @@
+// +build fixtures
+
 package buildinfo
 
 import (
diff --git a/openstack/orchestration/v1/stackevents/fixtures.go b/openstack/orchestration/v1/stackevents/fixtures.go
index 235787a..1004702 100644
--- a/openstack/orchestration/v1/stackevents/fixtures.go
+++ b/openstack/orchestration/v1/stackevents/fixtures.go
@@ -1,3 +1,5 @@
+// +build fixtures
+
 package stackevents
 
 import (
diff --git a/openstack/orchestration/v1/stackresources/fixtures.go b/openstack/orchestration/v1/stackresources/fixtures.go
index 952dc54..8f5df7d 100644
--- a/openstack/orchestration/v1/stackresources/fixtures.go
+++ b/openstack/orchestration/v1/stackresources/fixtures.go
@@ -1,3 +1,5 @@
+// +build fixtures
+
 package stackresources
 
 import (
diff --git a/openstack/orchestration/v1/stacks/fixtures.go b/openstack/orchestration/v1/stacks/fixtures.go
index 83f5dec..9c95a89 100644
--- a/openstack/orchestration/v1/stacks/fixtures.go
+++ b/openstack/orchestration/v1/stacks/fixtures.go
@@ -1,3 +1,5 @@
+// +build fixtures
+
 package stacks
 
 import (
diff --git a/openstack/orchestration/v1/stacktemplates/fixtures.go b/openstack/orchestration/v1/stacktemplates/fixtures.go
index fa9b301..ff544d4 100644
--- a/openstack/orchestration/v1/stacktemplates/fixtures.go
+++ b/openstack/orchestration/v1/stacktemplates/fixtures.go
@@ -1,3 +1,5 @@
+// +build fixtures
+
 package stacktemplates
 
 import (