fix admin clone method
add readme description about admin
describe basic commands and extension commands of admin
fix readme
add admin client test and sandbox
remove printfs
fix sandbox and add getpid test
fix admin clients, finish unittests, leave 3 functions untested because they are not supported in 0.24 server, needs to be tested on a newer server version
remove a comment
use pytest instead of testifycompat
Merge pull request #4 from paiweilai1984/paiwei-fix-admin-client

* update docs
* fix admin methods 
* add unittests for admin