Don't create unnecessary tenants in tenant tests

While creating the "venus" tenant for every test makes the code cleaner,
it also makes the tests much slower, so we aren't doing so in tests
where we don't use this tenant.

spec/system/multitenancy_spec.rb

@@ -1,12 +1,10 @@
 require "rails_helper"
 
 describe "Multitenancy", :seed_tenants do
-  before do
-    create(:tenant, schema: "mars")
-    create(:tenant, schema: "venus")
-  end
+  before { create(:tenant, schema: "mars") }
 
   scenario "Disabled features", :no_js do
+    create(:tenant, schema: "venus")
     Tenant.switch("mars") { Setting["process.debates"] = true }
     Tenant.switch("venus") { Setting["process.debates"] = nil }
 
@@ -22,6 +20,7 @@ describe "Multitenancy", :seed_tenants do
   end
 
   scenario "Content is different for differents tenants" do
+    create(:tenant, schema: "venus")
     Tenant.switch("mars") { create(:poll, name: "Human rights for Martians?") }
 
     with_subdomain("mars") do
@@ -69,6 +68,7 @@ describe "Multitenancy", :seed_tenants do
   end
 
   scenario "Creating content in one tenant doesn't affect other tenants" do
+    create(:tenant, schema: "venus")
     Tenant.switch("mars") { login_as(create(:user)) }
 
     with_subdomain("mars") do
@@ -96,6 +96,7 @@ describe "Multitenancy", :seed_tenants do
   end
 
   scenario "Users from another tenant cannot vote" do
+    create(:tenant, schema: "venus")
     Tenant.switch("mars") { create(:proposal, title: "Earth invasion") }
     Tenant.switch("venus") { login_as(create(:user)) }
 
@@ -138,6 +139,7 @@ describe "Multitenancy", :seed_tenants do
   end
 
   scenario "Users from another tenant can't sign in" do
+    create(:tenant, schema: "venus")
     Tenant.switch("mars") { create(:user, email: "marty@consul.dev", password: "20151021") }
 
     with_subdomain("mars") do