base-files: stage2: improve /proc/*/stat parser

base-files: stage2: improve /proc/*/stat parser

Simply reading /proc/*/stat as a space-separated string will not work
as the process name may itself contain spaces. Hence we must match on
the '(' and ')' characters around the process name and can then handle
the remaining string as space-separated values.
This fixes shell error messages which have been popping up the console
due to spaces in process names being interpreted as field separators.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>