Another batch of changes that should make the SST process
more reliable in all scenarios:

 1) Added hostname or CN verification when stunnel is used
    with certificate chain verification (verifyChain = yes);
 2) Added check for the absence of the stunnel utility for
    mtr tests;
 3) Deletion of working files before and after SST is done
    more accurately;
 4) rsync on joiner can be run even if the path to its
    configuration file contains spaces;
 5) More accurate directory creation (for data files and
    for logs);
 6) IST with mysqldump no longer turns off statement logging;
 7) Reset password for mysqldump when password is empty but
    username is specified;
 8) More reliable quoting when generating statements in
    wsrep_sst_mysqldump;
 9) Added explicit generation of 2048-bit Diffie-Hellman
    parameters for sockat < 1.7.3, by analogy with xtrabackup;
10) Compression parameters for qpress are read from all
    suitable server groups in configuration file, as well as
    from the [sst] and [xtrabackup] groups;
11) Added a test that checks compression using qpress;
12) Checking for optional utilities is modified to work even
    if they implemented as built-in shell commands (unlikely
    on real systems, but more reliable).