minor: read preference test fix

Secondary to remove is randomly chosen so test would randomly fail
before this fix.

test/replica_sets/read_preference_test.rb

@@ -42,7 +42,7 @@ class ReadPreferenceTest < Test::Unit::TestCase
     @rs.add_arbiter
     @rs.remove_secondary_node
     
-    @conn = ReplSetConnection.new(build_seeds(2), :read => :secondary_only)
+    @conn = ReplSetConnection.new(build_seeds(3), :read => :secondary_only)
 
     @db = @conn.db(MONGO_TEST_DB)
     @coll = @db.collection("test-sets")

test/tools/repl_set_manager.rb

@@ -152,6 +152,7 @@ class ReplSetManager
     end
 
     con.close
+    ensure_up
 
     return secondary
   end