Overwrite database pool size for logs database

Logs database config is set in travis keychain and is set to a
concurrency much higher than what we set in heroku config. I don't want
to change it globally, because it may need to be different for other
apps, so I'm changing it here just before we connect to the db.

lib/travis/api/app.rb

@@ -199,6 +199,9 @@ module Travis::Api
         Travis::Database.connect
 
         if Travis.config.logs_database
+          pool_size = ENV['DATABASE_POOL_SIZE']
+          Travis.config.logs_database[:pool] = pool_size if pool_size
+
           Log.establish_connection 'logs_database'
           Log::Part.establish_connection 'logs_database'
         end