Factor common code out of the test fake sources

* * *
More fake source refacoring

tests/flexnbd/fake_source.rb

@@ -0,0 +1,40 @@
+# encoding: utf-8
+
+require 'socket'
+require "timeout"
+require 'flexnbd/constants'
+
+module FlexNBD
+  module FakeSource
+
+    def connect( addr, port, err_msg )
+      timing_out( 2, err_msg ) do
+        TCPSocket.open( addr, port )
+      end
+    end
+
+
+    def read_hello( client_sock )
+      timing_out( FlexNBD::MS_HELLO_TIME_SECS,
+                  "Timed out waiting for hello." ) do
+          fail "No hello." unless (hello = client_sock.read( 152 )) &&
+            hello.length==152
+        hello
+      end
+    end
+
+
+    def timing_out( time, msg )
+      begin
+        Timeout.timeout( time ) do
+          yield
+        end
+      rescue Timeout::Error
+        $stderr.puts msg
+        exit 1
+      end
+    end
+
+
+  end # module FakeSource
+end # module FlexNBD