mariabackup.incremental_encrypted failed in buildbot with timeout

mariabackup.incremental_encrypted        w2 [ fail ]  timeout after 900 seconds

        Test ended at 2018-03-12 17:48:54

Test case timeout after 900 seconds

== /usr/local/mariadb-10.1.32-linux-x86_64/mysql-test/var/2/log/incremental_encrypted.log == 

call mtr.add_suppression("InnoDB: New log files created");

CREATE TABLE t(i INT) ENGINE INNODB ENCRYPTED=YES;

INSERT INTO t VALUES(1);

# Create full backup , modify table, then create incremental/differential backup

INSERT INTO t VALUES(2);

SELECT * FROM t;

i

1

2

# Prepare full backup, apply incremental one

 == /usr/local/mariadb-10.1.32-linux-x86_64/mysql-test/var/2/tmp/analyze-timeout-mysqld.1.err ==

mysqltest: Could not open connection 'default' after 500 attempts: 2002 Can't connect to local MySQL server through socket '/usr/local/mariadb-10.1.32-linux-x86_64/mysql-test/var/tmp/2/mysqld.1.sock' (111 "Connection refused")