Please allow other separators as comma

[bertwesarg]

For the DOMAINS variable here:

scorep_plugin_meric/src/meric_plugin.cpp

Line 51 in 168e9aa

for ( std::string name : split_string( env_str, ',' ) )

This allows to pass env variables to slurms --export flag. This flag is only allowed once and uses comma to separate multiple env variables with there values. Score-P already provides such a mean for other env variables via a SEP variable.