* fix windows compatibility and add windows unittest CI

* remote conda/pip source

* fix file type

* fix set variable

* close_fds is supported in 3.7+

* fix windows build script

* test dygraph first

* clean build directory

* fix add environment path repeatedly

* fix conda issues in linux unittest

* use get_free_tcp_port in get_set_attribute_test

* remove conda env folder

* rename filename