improve multi cmd_dir handling

[ghost]

the test if a command exists in a directory is now using an explicit glob pattern which doesn't match as well on similar commands

example situation:

mkdir /tmp/cmd1
mkdir /tmp/cmd2

touch /tmp/cmd1/my-command-special_pre.sh
touch /tmp/cmd2/my-command_pre.sh

athena.plugin.set_plg_cmd_dir "/tmp/cmd1:/tmp/cmd2"

calling it later via

athena myplugin my-command

will end up with

Unrecognized command or plugin 'my-command'.