Fix gparted not launching when PS_FORMAT environment variable set
pgrep(1) is not affected by environment variables such as
PS_FORMAT, so it is safe to use without assuming
PS_FORMAT is similar-enough to the default.
This is the root cause of Debian bug #864932, that caused a user who had
PS_FORMAT set to be unable to start
gparted, short of calling
gpartedbin directly, as
ps -e | grep gpartedbin matched the
Moreover, this is more efficient and less error-prone.