Etcd minor version mismatch between client and server

[ndegory]

The Etcd image used by AMP is as of this writing 3.0.12
The Etcd dependency in glide.yaml is ^3.1.0.alpha.1

Etcd 3.1 has made (minor) changes in the gRPC layer, there's a risk of miscommunication.

[ndegory]

changing the dependency to ~3.0 broke the build, make install complained about missing contants in the protobuf package. Moving to 3.1 (as intended) is probably a safe choice now that a RC is available.