test=develop

* improve save and load behaviour, test=develop

* code cleaning, test=develop

* disable check_guards and update_guards in release version, test=develop

* fix compilation issue, test=develop

* add buddy_allocator speed test data, test=develop

* fix compilation issue, test=develop

* fix comment, test=develop

* update function names according to the google C++ style guide, test=develop

* tweak the test data format, test=develop

* move buddy_allocator_test_data to paddle/fluid/testdata, test=develop

* add accessor and mutator for Desc, test=develop

* fix gpu_info, test=develop

* fix reserving gpu memory calculation bug, add fraction=1 unittest, test=develop

* fix bug again for reserving size, test=develop

GPU allocation uses fraction of available memory, also fix the GetUsed without lock