Get rid of deprecated /var/run paths

debian/mariadb-server-10.2.postinst

58:    # This is needed because mysql_install_db removes the pid file in /var/run

61:    # script fails. I can't tell at this point because of the cleaned /var/run.

67:    mysql_rundir=/var/run/mysqld

debian/mariadb-server-10.2.mysql.init

111:    test -e /var/run/mysqld || install -m 755 -o mysql -g root -d /var/run/mysqld

debian/mariadb-server-10.2.logcheck.ignore.server

2:/etc/init.d/mysql\[[0-9]+\]: Check that mysqld is running and that the socket: '/var/run/mysqld/mysqld.sock' exists\!$

debian/mariadb-server-10.2.logcheck.ignore.paranoid

1:/etc/init.d/mysql\[[0-9]+\]: Check that mysqld is running and that the socket: '/var/run/mysqld/mysqld.sock' exists\!$

5:mysqld\[[0-9]+\]: Version: .* socket: '/var/run/mysqld/mysqld.sock'  port: 3306$

debian/mariadb-server-10.2.logcheck.ignore.workstation

2:/etc/init.d/mysql\[[0-9]+\]: Check that mysqld is running and that the socket: '/var/run/mysqld/mysqld.sock' exists\!$

debian/additions/my.cnf

20:socket		= /var/run/mysqld/mysqld.sock

27:socket		= /var/run/mysqld/mysqld.sock

35:pid-file	= /var/run/mysqld/mysqld.pid

36:socket		= /var/run/mysqld/mysqld.sock

debian/mariadb-server-10.2.postrm

70:    rm -rf /var/run/mysqld # this directory is created by the init script, don't leave behind

storage/maria/ma_test_force_start.pl

57:my $server_pid_name="./var/run/master.pid";

support-files/policy/apparmor/usr.sbin.mysqld

57:  /var/run/mysqld/mysqld.pid w,

58:  /var/run/mysqld/mysqld.sock w,

libmariadb/.travis/build/Dockerfile

66:    	&& rm -rf /var/lib/mysql && mkdir -p /var/lib/mysql /var/run/mysqld \

67:    	&& chown -R mysql:mysql /var/lib/mysql /var/run/mysqld \

68:    	&& chmod 777 /var/run/mysqld \

cmake/systemd.cmake

59:          SET(SYSTEMD_EXECSTARTPRE "ExecStartPre=/usr/bin/install -m 755 -o mysql -g root -d /var/run/mysqld")

cmake/install_layout.cmake

187:SET(INSTALL_UNIX_ADDRDIR_DEB            "/var/run/mysqld/mysqld.sock")