Allow other custom mysqld than mysqld-debug

[ogrovlen]

Only require the debug plugin directory when the custom mysqld actually is "mysqld-debug"

[datacharmer]

Thanks for your contribution.
However, I can't figure out the actual difference between my code and your proposal.
Could you provide a sample command line with the expected result?

[ogrovlen]

$ ./dbdeployer deploy single 8.0.23 --my-cnf-file ../tpchcomp/config/mysql.cnf --custom-mysqld mysqld-bind-cpu
error creating sandbox: 'the request of using mysqld-debug can't be honored.
This deployment is using a plugin, but the debug
directory for plugins was not found'
$ git checkout custom_mysqld_fix
Switched to branch 'custom_mysqld_fix'
Your branch is up to date with 'origin/custom_mysqld_fix'.
$ go build
$ ./dbdeployer deploy single 8.0.23 --my-cnf-file ../tpchcomp/config/mysql.cnf --custom-mysqld mysqld-bind-cpu
Database installed in $HOME/sandboxes/msb_8_0_23
run 'dbdeployer usage single' for basic instructions'
.............. sandbox server started

AFAICT from the code, if I specify --custom-mysqld with something else than "mysqld_debug", rightPluginDir will be set to false.