Retry failed rebind attempts

When we receive a migration, if rebinding to the new listen address and
port fails for a reason which might be fixable, rather than killing the
server we retry once a second.  Also in this patch: non-overlapping log
messages and a fix for the client going away halfway through a sendfile
loop.

tests/acceptance/fakes/source/close_after_entrust_reply.rb

@@ -9,7 +9,7 @@
 require 'flexnbd/fake_source'
 include FlexNBD
 
-addr, port, srv_pid = *ARGV
+addr, port, srv_pid, rebind_addr, rebind_port = *ARGV
 
 client = FakeSource.new( addr, port, "Timed out connecting" )
 client.read_hello
@@ -25,8 +25,8 @@ sleep(0.25)
 client2 = FakeSource.new( addr, port, "Timed out reconnecting to mirror" )
 client2.send_mirror
 
-sleep(0.25)
-client3 = FakeSource.new( addr, port, "Timed out reconnecting to read" )
+sleep(1)
+client3 = FakeSource.new( rebind_addr, rebind_port, "Timed out reconnecting to read" )
 client3.close
 
 exit(0)

tests/acceptance/fakes/source/close_mid_read.rb

@@ -0,0 +1,17 @@
+#!/usr/bin/env ruby
+
+# Connect, but get the protocol wrong: don't read the hello, so we
+# close and break the sendfile.
+
+require 'flexnbd/fake_source'
+include FlexNBD
+
+addr, port, srv_pid, newaddr, newport = *ARGV
+
+client = FakeSource.new( addr, port, "Timed out connecting" )
+client.write_read_request( 0, 8 )
+client.read_raw( 4 )
+client.close
+
+
+exit(0)

tests/acceptance/fakes/source/successful_transfer.rb

@@ -0,0 +1,29 @@
+#!/usr/bin/env ruby
+
+# Successfully send a migration, but squat on the IP and port which
+# the destination wants to rebind to.  The destination should retry
+# every second, so we give it up then attempt to connect to the new
+# server.
+
+require 'flexnbd/fake_source'
+include FlexNBD
+
+addr, port, srv_pid, newaddr, newport = *ARGV
+
+squatter = TCPServer.open( newaddr, newport.to_i )
+
+client  = FakeSource.new( addr, port, "Timed out connecting" )
+client.send_mirror()
+
+sleep(1)
+
+squatter.close()
+
+sleep(1)
+
+client2 = FakeSource.new( newaddr, newport.to_i, "Timed out reconnecting" )
+client2.read_hello
+client2.read( 0, 8 )
+client2.close
+
+exit( 0 )