guests/coreos: Do not use sudo for looking up hostname

plugins/guests/coreos/cap/change_host_name.rb

@@ -3,10 +3,16 @@ module VagrantPlugins
     module Cap
       class ChangeHostName
         def self.change_host_name(machine, name)
-          machine.communicate.tap do |comm|
-            if !comm.test("sudo hostname --fqdn | grep '#{name}'")
-              comm.sudo("hostname #{name.split('.')[0]}")
-            end
+          comm = machine.communicate
+
+          if !comm.test("hostname --fqdn | grep -w '#{name}'")
+            basename = name.split(".", 2)[0]
+            comm.sudo("hostname '#{basename}'")
+
+            # Note that when working with CoreOS, we explicitly do not add the
+            # entry to /etc/hosts because this file does not exist on CoreOS.
+            # We could create it, but the recommended approach on CoreOS is to
+            # use Fleet to manage /etc/hosts files.
           end
         end
       end

test/unit/plugins/guests/coreos/cap/change_host_name_test.rb

@@ -9,29 +9,29 @@ describe "VagrantPlugins::GuestCoreOS::Cap::ChangeHostName" do
   end
 
   let(:machine) { double("machine") }
-  let(:communicator) { VagrantTests::DummyCommunicator::Communicator.new(machine) }
+  let(:comm) { VagrantTests::DummyCommunicator::Communicator.new(machine) }
 
   before do
-    allow(machine).to receive(:communicate).and_return(communicator)
+    allow(machine).to receive(:communicate).and_return(comm)
   end
 
   after do
-    communicator.verify_expectations!
+    comm.verify_expectations!
   end
 
   describe ".change_host_name" do
-    let(:hostname) { "example.com" }
+    let(:hostname) { "banana-rama.example.com" }
 
     it "sets the hostname" do
-      communicator.stub_command("sudo hostname --fqdn | grep '#{hostname}'", exit_code: 1)
-      communicator.expect_command("hostname example")
+      comm.stub_command("hostname --fqdn | grep -w '#{hostname}'", exit_code: 1)
+      comm.expect_command("hostname 'banana-rama'")
       described_class.change_host_name(machine, hostname)
     end
 
     it "does not change the hostname if already set" do
-      communicator.stub_command("sudo hostname --fqdn | grep '#{hostname}'", exit_code: 0)
+      comm.stub_command("hostname --fqdn | grep -w '#{hostname}'", exit_code: 0)
       described_class.change_host_name(machine, hostname)
-      expect(communicator.received_commands.size).to eq(1)
+      expect(comm.received_commands.size).to eq(1)
     end
   end
 end