Close idle conns when closing consul topo

[timvaillancourt]

Description

The *api.Config struct for the Consul client (in go/vt/topo/consultopo) holds a *http.Transport in the config, which is long-lived 😕

This object being in the "config" can cause idle connections to be left open when .Close() is called on the Consul topo implementation, which currently does nothing with the *http.Transport. This usually won't matter - the idle conn will eventually get closed, but the fact all connections are not closed on .Close() can cause unit test failures Slack sees on a yet-to-upstream patch

This PR:

1. Calls .CloseIdleConnections() on the *http.Transport in the .Close() of the consul topo. This ensures that the idle connections the long-lived *http.Transport holds are closed
2. Add a defer topoServer.Close() to the .Setup() method in go/vt/vttest/topoctl.go - this topoServer is only used in .Setup() and has no .Close() call today

Related Issue(s)

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