LP1378355 - Pass the value of --defaults-group-suffix to xtrabackup duri...

...ng SST

MTR starts all nodes with a shared my.cnf file with individual sections per-server. In order for xtrabackup SST to work in such an environment, xtrabackup must be passed the name of the section so that it can retrieve the innodb parameters from it.

This option was added to xtrabackup version 2.0.1 in  Jul 07 2012, so this change will break compatibility with  older versions of xtrabackup.

MySQL provides the name of the section as a suffix, e.g. ".2" and xtrabackup requires the full name, e.g. "mysqld.2". So the bash script will concatenate mysqld to .2 to produce the format required by xtrabackup. If there is no dedicated section, and no suffix, the default will be "mysqld".