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).
