Fix two bugs causing multiplayer tests to fail

After finding a game, in some circumstances the join script got the
leader select dialog after only yielding once. Because the loop that
checks when the dialog appears was a repeat-until loop and not a while
loop, it was always run at least once, making the script yield even when
the dialog was already shown. That caused the dialog to close with a
"not shown" status that resulted in exiting the game.

MP tests run two games, not one. A MP wait screen is shown between the
games to the joining player (but not to the host, see
src/game_initialization/playcampaign.cpp:352 ). The join script ended up
quitting between the games. Fixed by simply duplicating code to make the
join script play two games.

join.lua

@@ -93,7 +93,7 @@ local function plugin()
 
   events, context, info = coroutine.yield()
 
-  repeat
+  while not (info.name == "Dialog" or info.name == "Multiplayer Wait") do
     if context.join then
       context.join({})
     else
@@ -102,7 +102,7 @@ local function plugin()
 
     events, context, info = coroutine.yield()
     idle_text("in " .. info.name .. " waiting for leader select dialog")
-  until info.name == "Dialog" or info.name == "Multiplayer Wait"
+  end
 
   if info.name == "Dialog" then
     log("got a leader select dialog...")
@@ -130,6 +130,16 @@ local function plugin()
     idle_text("in " .. info.name .. " waiting for not game")
   until info.name ~= "Game"
 
+  repeat
+    events, context, info = coroutine.yield()
+    idle_text("in " .. info.name .. " waiting for game")
+  until info.name == "Game"
+
+  repeat
+    events, context, info = coroutine.yield()
+    idle_text("in " .. info.name .. " waiting for not game")
+  until info.name ~= "Game"
+
   log("left a game context...")
 
   repeat