net/rpc: call client.Close() when test exit
net/rpc: call client.Close() when test exit

Fixes issue 5768.

R=golang-dev
CC=golang-dev
https://codereview.appspot.com/10503043

Committer: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@golang.org>

gnanderson/go,gnanderson/go,gnanderson/go,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,gnanderson/go,tv42/old-go,apparentlymart/golang,apparentlymart/golang,pombredanne/go-deleteme,pombredanne/go-deleteme,apparentlymart/golang,apparentlymart/golang,gnanderson/go,gnanderson/go,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,apparentlymart/golang,tv42/old-go,gnanderson/go,apparentlymart/golang,pombredanne/go-deleteme,tv42/old-go,tv42/old-go,tv42/old-go,apparentlymart/golang