bootchart: put the bootchart into the journal.
This bit of code is mostly stolen from coredump.c. We construct
a simple journal message and append the bootchart file in the
journal automatically.
You can extract the latest bootchart from the current boot with
something like:
$ journalctl -b MESSAGE_ID=
9f26aa562cf440c2b16c773d0479b518 --field=BOOTCHART
which prints it to stdout.
None of the other logic is touched. The journal entry is created
even if bootchart was run manually, which is probably wrong.