Add fixtures build tag to all fixtures.go files

Ensure testing dependencies from fixtures don't leak into builds.
diff --git a/openstack/db/v1/configurations/fixtures.go b/openstack/db/v1/configurations/fixtures.go
index ae65416..9064c6c 100644
--- a/openstack/db/v1/configurations/fixtures.go
+++ b/openstack/db/v1/configurations/fixtures.go
@@ -1,3 +1,5 @@
+// +build fixtures
+
 package configurations
 
 import (
diff --git a/openstack/db/v1/databases/fixtures.go b/openstack/db/v1/databases/fixtures.go
index 3e67721..8d21e90 100644
--- a/openstack/db/v1/databases/fixtures.go
+++ b/openstack/db/v1/databases/fixtures.go
@@ -1,3 +1,5 @@
+// +build fixtures
+
 package databases
 
 import (
diff --git a/openstack/db/v1/datastores/fixtures.go b/openstack/db/v1/datastores/fixtures.go
index fd767cd..eb796eb 100644
--- a/openstack/db/v1/datastores/fixtures.go
+++ b/openstack/db/v1/datastores/fixtures.go
@@ -1,3 +1,5 @@
+// +build fixtures
+
 package datastores
 
 import (
diff --git a/openstack/db/v1/flavors/fixtures.go b/openstack/db/v1/flavors/fixtures.go
index f0016bc..9839324 100644
--- a/openstack/db/v1/flavors/fixtures.go
+++ b/openstack/db/v1/flavors/fixtures.go
@@ -1,3 +1,5 @@
+// +build fixtures
+
 package flavors
 
 import (
diff --git a/openstack/db/v1/instances/fixtures.go b/openstack/db/v1/instances/fixtures.go
index af7b185..eb1da6a 100644
--- a/openstack/db/v1/instances/fixtures.go
+++ b/openstack/db/v1/instances/fixtures.go
@@ -1,3 +1,5 @@
+// +build fixtures
+
 package instances
 
 import (
diff --git a/openstack/db/v1/users/fixtures.go b/openstack/db/v1/users/fixtures.go
index 516b335..f5a4cc1 100644
--- a/openstack/db/v1/users/fixtures.go
+++ b/openstack/db/v1/users/fixtures.go
@@ -1,3 +1,5 @@
+// +build fixtures
+
 package users
 
 import (