MDEV-21770: `galera_3nodes.galera_ipv6_mariabackup` fails
This patch fixes several flaws in the SST scripts that cause
failures while running tests that use version 6 IP addresses
for cluster nodes.
First, if the netcat utility is used for streaming (but not socat),
then in accordance with its command line syntax, we need to remove
the square brackets around the IPv6 address. However, for socat,
the address must contain square brackets, as before.
Secondly, if an IPv6 address is used, then from the joiner side for
a number of systems (such as Debian) we need to explicitly specify
the "-6" option, otherwise a listening socket with an IPv6 address
may not be created.
This patch also contains code improvements in the wsrep_sst_common.
Changed the code that pars the connection address - fixed the
shortcomings that sometimes led to incorrect parsing of parameters
when using shells other than the latest versions of bash.
Also, this patch removes the duplicate code that is intended
for parsing the connection address and which was located in the
wsrep_sst_mariabackup file, since all the necessary actions have
already been done in wsrep_sst_common and there they are done in
such a way that any shell is supported, not just bash.
The fix does not require separate tests, since all the
necessary tests are already present in the galera_3nodes suite.
On the contrary, after this fix, tests using IPv6 addresses can
be removed from the disabled list (this will be done in a separate
commit related to MDEV-23659).
