Fix test failure when run from DNS hijacked ISP

Removes the tld from 'unreachable host' to circumvent DNS hijacking
ISPs returning a 200 response for non-existent domains.

Fixes elastic#7124

spec/unit/plugin_manager/pack_fetch_strategy/repository_spec.rb

@@ -33,7 +33,7 @@
   context "when the remote host is unreachable" do
     it "returns false and yield a debug message" do
       # To make sure we really try to connect to a failing host we have to let it through webmock
-      host ="#{Time.now.to_i.to_s}-do-not-exist.com"
+      host ="#{Time.now.to_i.to_s}-do-not-exist"
       WebMock.disable_net_connect!(:allow => host)
       ENV["LOGSTASH_PACK_URL"] = "http://#{host}"
       expect(subject.get_installer_for(plugin_name)).to be_falsey