runner: Allow multiple --hook options

Test binaries now allow passing multiple --hook options, it just makes
sense that igt_runner follows suit, so let's do it.

Note that this requires having another file in the results directory for
storing the hook strings, as metadata.txt does not support multivalued
items.

Since we are using a different file to store hook strings, take this
opportunity to also allow multiline hook strings (which was not possible
with metadata.txt).

Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Gustavo Sousa <gustavo.sousa@intel.com>
Link: https://lore.kernel.org/r/20240814204822.95283-7-gustavo.sousa@intel.com


Signed-off-by: Matt Roper <matthew.d.roper@intel.com>