cipd: Implement local cache for ResolveVersion(...) call with tags.

go/src/infra/tools/cipd/apps/cipd/friendly.go

Index: go/src/infra/tools/cipd/apps/cipd/friendly.go
diff --git a/go/src/infra/tools/cipd/apps/cipd/friendly.go b/go/src/infra/tools/cipd/apps/cipd/friendly.go
index b3769580f8ff0ead1183e6eeb6218cf2a18d2f94..2086997a01f5980ec265f76edf1e3aea2a4724f2 100644
--- a/go/src/infra/tools/cipd/apps/cipd/friendly.go
+++ b/go/src/infra/tools/cipd/apps/cipd/friendly.go
@@ -204,6 +204,14 @@ func (site *installationSite) initClient(authFlags authcli.Flags) (err error) {
 	return
 }
 
+// closeClient closes the underlying cipd.Client if necessary.
+func (site *installationSite) closeClient() {
+	if site.client != nil {
+		site.client.Close()
+		site.client = nil
+	}
+}
+
 // modifyConfig reads config file, calls callback to mutate it, then writes
 // it back.
 func (site *installationSite) modifyConfig(cb func(cfg *installationSiteConfig) error) error {
@@ -457,6 +465,7 @@ func (c *installRun) Run(a subcommands.Application, args []string) int {
 	if err = site.initClient(c.authFlags); err != nil {
 		return c.done(nil, err)
 	}
+	defer site.closeClient()
 
 	return c.done(site.installPackage(pkgName, version, c.force))
 }