Consul-rust does not reuse reqwest clients

[mtthw-meyer]

When making many requests I'm getting 104s from consul. I suspect the root cause it not reusing reqwest clients.

https://github.com/seanmonstar/reqwest/blob/0fc1652975a3083843a6a0d5be5c8f23e296a6e5/src/lib.rs#L47