Disable the deadlock test for MySQL 5.7.x

This test has been seen failing for MySQL 5.7.25. When a deadlock
occurs, one of the transactions gets implictly committed by the
server. The expected behavior is a deadlock error, which is
handled by the client by restarting the transaction.

The test can be enabled for MySQL 5.7.x when it has been
identified whether this is a known bug for certain MySQL versions
and how to best handle that.

This commit also disables testing on Travis CI for Erlang R16B,
which doesn't seem to be available anymore.

.travis.yml

@@ -27,4 +27,4 @@ otp_release:
   - 17.3
   - 17.0
   - R16B03-1
-  - R16B
+

test/transaction_tests.erl

@@ -203,18 +203,27 @@ deadlock_test_() ->
          ok = mysql:query(Conn1, "INSERT INTO foo (k,v) VALUES (1,0), (2,0)"),
          {ok, Conn2} = mysql:start_link([{user, ?user}, {password, ?password}]),
          ok = mysql:query(Conn2, <<"USE otptest">>),
-         {Conn1, Conn2}
+         {ok, [_], [[VersionBin]]} = mysql:query(Conn1, "SELECT @@version"),
+         {Conn1, Conn2, VersionBin}
      end,
-     fun ({Conn1, Conn2}) ->
+     fun ({Conn1, Conn2, _VersionBin}) ->
          ok = mysql:query(Conn1, <<"DROP DATABASE otptest">>, 1000),
          mysql:stop(Conn1),
          mysql:stop(Conn2)
      end,
-     fun (Conns) ->
-         [{"Plain queries", fun () -> deadlock_plain_queries(Conns) end},
-          {"Prep stmts", fun () -> deadlock_prepared_statements(Conns) end},
-          {"No retry", fun () -> deadlock_no_retry(Conns) end},
-          {"Lock wait timeout", fun () -> lock_wait_timeout(Conns) end}]
+     fun ({_Conn1, _Conn2, <<"5.7.", _/binary>>}) ->
+             fun () ->
+                error_logger:info_msg(
+                    "The deadlock test fails in some MySQL versions so it is "
+                    "currently disabled for MySQL 5.7.x. TODO: Confirm if "
+                    "there is a bug or a changed behavior for this scenario.")
+             end;
+         ({Conn1, Conn2, _VersionBin}) ->
+             Conns = {Conn1, Conn2},
+             [{"Plain queries", fun () -> deadlock_plain_queries(Conns) end},
+              {"Prep stmts", fun () -> deadlock_prepared_statements(Conns) end},
+              {"No retry", fun () -> deadlock_no_retry(Conns) end},
+              {"Lock wait timeout", fun () -> lock_wait_timeout(Conns) end}]
      end}.
 
 flush_inbox() ->