perf(dracut-functions): optimize inst_libdir_file()

[aafeijoo-suse]

Let's start analyzing the output of a non-hostonly build, focusing on the inst_libdir_file() calls:

$ dracut -f -N --debug testn.img 2>&1 &> testn.txt
$ grep -r -c "(inst_libdir_file): inst_multiple" testn.txt
17
$ grep -r "(inst_libdir_file): inst_multiple" testn.txt | awk -F"inst_multiple " '{ print $2 }' | tr ' ' '\n' | sort | wc -l
295
$ grep -r "(inst_libdir_file): inst_multiple" testn.txt | awk -F"inst_multiple " '{ print $2 }' | tr ' ' '\n' | sort -u | wc -l
201

There are 94 files that are attempted to be installed multiple times. After adding a simple cache:

$ grep -r -c "(inst_libdir_file): inst_multiple" testn2.txt
13
$ grep -r "(inst_libdir_file): inst_multiple" testn2.txt | awk -F"inst_multiple " '{ print $2 }' | tr ' ' '\n' | sort | wc -l
201

Checklist

• I have tested it locally
• I have reviewed and updated any documentation if relevant
• I am providing new code and test(s) for it

[bdrung]

I would prefer to aim for a bigger improvement: Instead of caching on individual file level, I would go one step further for #1419: Add staging functions similar to the inst_* functions. These functions would just collect what should be added. Then call an dracut-intsall equivalent to only write a manifest for 3cpio.