MDEV 4427: query timeouts

Added MAX_STATEMENT_TIME user variable to automaticly kill queries after a given time limit has expired.

- Added timer functions based on pthread_cond_timedwait
- Added kill_handlerton() to signal storage engines about kill/timeout
- Added support for GRANT ... MAX_STATEMENT_TIME=#
- Copy max_statement_time to current user, if stored in mysql.user
- Added status variable max_statement_time_exceeded
- Added KILL_TIMEOUT
- Removed digest hash from performance schema tests as they change all the time.
- Updated test results that changed because of the new user variables or new fields in mysql.user

This functionallity is inspired by work done by Davi Arnaut at twitter.
Test case is copied from Davi's work.

Documentation can be found at
https://kb.askmonty.org/en/how-to-limittimeout-queries/

mysql-test/r/mysqld--help.result:
  Updated for new help message
mysql-test/suite/perfschema/r/all_instances.result:
  Added new mutex
mysql-test/suite/sys_vars/r/max_statement_time_basic.result:
  Added testing of max_statement_time
mysql-test/suite/sys_vars/t/max_statement_time_basic.test:
  Added testing of max_statement_time
mysql-test/t/max_statement_time.test:
  Added testing of max_statement_time
mysys/CMakeLists.txt:
  Added thr_timer
mysys/my_init.c:
mysys/mysys_priv.h:
  Added new mutex and condition variables
  Added new mutex and condition variables
mysys/thr_timer.c:
  Added timer functions based on pthread_cond_timedwait()
  This can be compiled with HAVE_TIMER_CREATE to benchmark agains timer_create()/timer_settime()
sql/lex.h:
  Added MAX_STATEMENT_TIME
sql/log_event.cc:
  Safety fix (timeout should be threated as an interrupted query)
sql/mysqld.cc:
  Added support for timers
  Added status variable max_statement_time_exceeded
sql/share/errmsg-utf8.txt:
  Added ER_QUERY_TIMEOUT
sql/signal_handler.cc:
  Added support for KILL_TIMEOUT
sql/sql_acl.cc:
  Added support for GRANT ... MAX_STATEMENT_TIME=#
  Copy max_statement_time to current user
sql/sql_class.cc:
  Added timer functionality to THD.
  Added thd_kill_timeout()
sql/sql_class.h:
  Added timer functionality to THD.
  Added KILL_TIMEOUT
  Added max_statement_time variable in similar manner as long_query_time was done.
sql/sql_connect.cc:
  Added handling of max_statement_time_exceeded
sql/sql_parse.cc:
  Added starting and stopping timers for queries.
sql/sql_show.cc:
  Added max_statement_time_exceeded for user/connects status in MariaDB 10.0
sql/sql_yacc.yy:
  Added support for GRANT ... MAX_STATEMENT_TIME=# syntax, to be enabled in 10.0
sql/structs.h:
  Added max_statement_time user resource
sql/sys_vars.cc:
  Added max_statement_time variables
mysql-test/suite/roles/create_and_drop_role_invalid_user_table.test
  Removed test as we require all fields in mysql.user table.
scripts/mysql_system_tables.sql
scripts/mysql_system_tables_data.sql
scripts/mysql_system_tables_fix.sql
  Updated mysql.user with new max_statement_time field

mysql-test/suite/funcs_1/r/is_columns_mysql.result

@@ -227,6 +227,7 @@ def	mysql	user	is_role	44	N	NO	enum	1	3	NULL	NULL	NULL	utf8	utf8_general_ci	enum
 def	mysql	user	Lock_tables_priv	21	N	NO	enum	1	3	NULL	NULL	NULL	utf8	utf8_general_ci	enum('N','Y')			select,insert,update,references	
 def	mysql	user	max_connections	39	0	NO	int	NULL	NULL	10	0	NULL	NULL	NULL	int(11) unsigned			select,insert,update,references	
 def	mysql	user	max_questions	37	0	NO	int	NULL	NULL	10	0	NULL	NULL	NULL	int(11) unsigned			select,insert,update,references	
+def	mysql	user	max_statement_time	46	0.000000	NO	decimal	NULL	NULL	12	6	NULL	NULL	NULL	decimal(12,6)			select,insert,update,references	
 def	mysql	user	max_updates	38	0	NO	int	NULL	NULL	10	0	NULL	NULL	NULL	int(11) unsigned			select,insert,update,references	
 def	mysql	user	max_user_connections	40	0	NO	int	NULL	NULL	10	0	NULL	NULL	NULL	int(11)			select,insert,update,references	
 def	mysql	user	Password	3		NO	char	41	41	NULL	NULL	NULL	latin1	latin1_bin	char(41)			select,insert,update,references	
@@ -568,3 +569,4 @@ NULL	mysql	user	max_user_connections	int	NULL	NULL	NULL	NULL	int(11)
 3.0000	mysql	user	password_expired	enum	1	3	utf8	utf8_general_ci	enum('N','Y')
 3.0000	mysql	user	is_role	enum	1	3	utf8	utf8_general_ci	enum('N','Y')
 3.0000	mysql	user	default_role	char	80	240	utf8	utf8_bin	char(80)
+NULL	mysql	user	max_statement_time	decimal	NULL	NULL	NULL	NULL	decimal(12,6)