Extend metadata_column_to_perfdata to Multiple Columns

[michaelmckinsey1]

Summary

Overdue improvements to the metadata_column_to_perfdata Function, mainly enabling adding multiple columns to the performance data table at the same time:

1. Enable adding several metadata_columns with one function call.
2. Rename to metadata_columns_to_perfdata to reflect functionality.
3. Add join_key argument to enable the usage of a different key to join on.
4. Improve the unit testing
5. Add extra error check for presence of join_key

Example

develop

tk.metadata_column_to_perfdata("variant")
tk.metadata_column_to_perfdata("tuning")
tk.metadata_column_to_perfdata("problemsize")
tk.metadata_column_to_perfdata("num_procs")

#216

tk.metadata_columns_to_perfdata(["variant", "tuning", "problemsize", "num_procs"])