Split CPE file to reduce sync memory usage (9.0)

[mattmundell]

This reduces the maximum amount of memory used by the CPE update during the SCAP sync, by parsing 40Mb chunks of the CPE dictionary at a time, instead of parsing the whole 162Mb dictionary.

My gvmd sync process is now maxing at about 3.5% of 16GB where it was 9% before.

gvmd creates the chunks itself, in a temp directory, using system to run a shell command. Not the best, but g_spawn_sync has trouble here because we're already handling child signals (because we've forked a process to run the sync). Also the XML wrapper replacements done by the shell command would be tedious to do in C.

This also add details to the proctitle during sync to make it easier to see where memory is spiking.

Checklist:

• Tests
• CHANGELOG Entry