Allow using glob pattern in the command list in configuration. This enables for
example placing all commands in a single directory and using /path/to/dir/*.sh
as one of the commands to run all shell scripts in that directory.
Glob patterns are applied on every run of the commands, so matching commands can
be added without restarting telegraf.
This constitutes a large change in how we will parse different data
formats going forward (for the plugins that support it)
This is working off @henrypfhu's changes.
Jari Sukanen
Thibault Cohen
Cameron Sparr
Henry Hu
Jack Zampolin
Philip Silva