Previously the ramdisk logs were only stored if the ramdisk reported an error.
However, we are moving from ramdisk-side validation to server-side, so we need
ramdisk logs to be available if processing fails too.
This change moves storing ramdisk logs from a ramdisk_error plugin to core
processing code. As before, it can be disabled by setting ramdisk_logs_dir to
an empty value.
Change-Id: Ib3742ee1c1d4f2f96d29466626e1121694610dc3
Closes-Bug: #1564448