meta-tizen: pam: fix shell tests on package install

meta-tizen: pam: fix shell tests on package install

Without this change you will may able to create an image
with this silent error :

  | Output from pam-*@*:
  | /*/rootfs/install/tmp/rpm-tmp.*: 4: [: x$D: unexpected operator
  | /*/rootfs/install/tmp/rpm-tmp.*: 5: [: -a: unexpected operator

Change-Id: Idbdafd3a05309a479d00f50ab0ae62cd28ddffff
(From meta-tizen rev: 5fa37bc13d0dc3a96f93dc93f378194826f64e47)
Signed-off-by: Philippe Coval <philippe.coval@osg.samsung.com>
Signed-off-by: Leon Anavi <leon.anavi@konsulko.com>