Remove usage of redis multi from api

This change removes usage of redis multi from API. Without this change the redis usage can cause issues because no connection pool is used, so another worker may try to use the same backend object causing a failure.

lib/vmpooler/api/v1.rb

@@ -163,18 +163,15 @@ module Vmpooler
     end
 
     def return_vm_to_ready_state(template, vm)
-      backend.multi
       backend.srem("vmpooler__migrating__#{template}", vm)
       backend.hdel("vmpooler__active__#{template}", vm)
       backend.hdel("vmpooler__vm__#{vm}", 'checkout', 'token:token', 'token:user')
       backend.smove("vmpooler__running__#{template}", "vmpooler__ready__#{template}", vm)
-      backend.exec
     end
 
     def account_for_starting_vm(template, vm)
       user = backend.hget("vmpooler__token__#{request.env['HTTP_X_AUTH_TOKEN']}", 'user')
       has_token_result = has_token?
-      backend.multi
       backend.sadd("vmpooler__migrating__#{template}", vm)
       backend.hset("vmpooler__active__#{template}", vm, Time.now)
       backend.hset("vmpooler__vm__#{vm}", 'checkout', Time.now)
@@ -187,7 +184,6 @@ module Vmpooler
           backend.hset("vmpooler__vm__#{vm}", 'lifetime', config['vm_lifetime_auth'].to_i)
         end
       end
-      backend.exec
     end
 
     def update_result_hosts(result, template, vm)