diagnostics: switch to shasum, filter sysinfo using lines

shasum seems more widely available than md5/md5sum, and we don't have to worry about dealing with the different signatures and output formats of md5 and md5sum then.

sysinfo outputs localized message labels, so we can't just grep for "OS Type". But OS is the first thing it outputs, so we can probably just grab those lines by line number. Switched to doing that.