base-passwd.preinst:fix creating passwd and group error

base-passwd.preinst:fix creating passwd and group error

Create files `passwd' and `group' in `$D${sysconfdir}', if `$D${sysconfdir}'
does not exist, there is an error:
...
cannot create $D${sysconfdir}/passwd: Directory nonexistent
cannot create $D${sysconfdir}/group: Directory nonexistent
...

Attampt to create dir before file creation.

[YOCTO #3917]

Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>