run-postinsts: Replace pi_dir variable test
Since commit
5159ddcb62682e1b7e63a20a9218ea96e3fe10a2 string length test
performed against pi_dir has effectively never been able to succeed.
Change this to rather test if pi_dir is not an existing directory. By
doing we remove the chance of seeing the following console error message
during first boot to a pristine rootfs:
'ls: /etc/ipk-postinsts: No such file or directory'
Signed-off-by: Niko Mauno <niko.mauno@iki.fi>
Signed-off-by: Ross Burton <ross.burton@intel.com>
