Move the nested groups seed behind an environment flag

This seed downloads 2.1 GB worth of repositories. Google can afford the
bandwidth, but if a person using the GDK is on a metered connection,
that's not so great.

Also the GDK test suite runs this seed, so every CI run for that project
had to download those as well. Needlessly wasteful.

db/fixtures/development/17_cycle_analytics.rb

@@ -223,7 +223,9 @@ class Gitlab::Seeder::CycleAnalytics
 end
 
 Gitlab::Seeder.quiet do
-  if ENV['SEED_CYCLE_ANALYTICS']
+  flag = 'SEED_CYCLE_ANALYTICS'
+
+  if ENV[flag]
     Project.all.each do |project|
       seeder = Gitlab::Seeder::CycleAnalytics.new(project)
       seeder.seed!
@@ -235,6 +237,6 @@ Gitlab::Seeder.quiet do
     seeder = Gitlab::Seeder::CycleAnalytics.new(Project.order(:id).first, perf: true)
     seeder.seed_metrics!
   else
-    puts "Not running the cycle analytics seed file. Use the `SEED_CYCLE_ANALYTICS` environment variable to enable it."
+    puts "Skipped. Use the `#{flag}` environment variable to enable."
   end
 end

db/fixtures/development/20_nested_groups.rb

@@ -27,6 +27,9 @@ end
 
 Sidekiq::Testing.inline! do
   Gitlab::Seeder.quiet do
+    flag = 'SEED_NESTED_GROUPS'
+
+    if ENV[flag]
       project_urls = [
         'https://android.googlesource.com/platform/hardware/broadcom/libbt.git',
         'https://android.googlesource.com/platform/hardware/broadcom/wlan.git',
@@ -65,5 +68,8 @@ Sidekiq::Testing.inline! do
           print 'F'
         end
       end
+    else
+      puts "Skipped. Use the `#{flag}` environment variable to enable."
+    end
   end
 end