* fix save/load in fleet (#17675)

* fix save/load in Fleet
* add UT framework of Fleet (#18058)

* add paddle cloud role maker for customized usage, note this is only for industrial users that have cloud environment pre-configuration (#18121)

add paddle cloud role maker for specific cloud usage. This pr will simplifies user's configuration in distributed training.

* assign role_maker before use (#18137)

* remove attribute in Allocator::Allocate, test=develop

* fix travis ci error, test=develop

Async exe support communicator

test=develop

* optimize communicator flag

* change flags in init py test=develop

test=develop