etcdserver: move newTestMember* to member_test.go
etcdserver: remove unnecessary newTestMemberp
etcdserver: use member pointer for all tests
Merge pull request #1688 from xiang90/cluster_test

Cluster test
*: support updating advertise-peer-url
Users might want to update the peerurl of the etcd member in several cases.
For example, if the IP address of the physical machine etcd running on is
changed, user need to update the adversite-pee-rurl accordingly.
This commit makes etcd support updating the advertise-peer-url of its members.