Add support for optional field in /proc/self/status

There's a "seccmp:" field that may or may not be included in the
/proc/self/status files, depending on kernel options.  With this
update the handler will do the right thing if the line is there or
not.  And since there's a new parse field, the JSON/CSV files used
by verification scripts had to be updated.
Make recreator for /proc/self/status able to deal with an optional field