base-files: Create /var/preferences

:Release Notes:
Create /var/preferences with mode 755 to protect the directory's
files from being removed or modified. In https://g2g.palm.com/3903,
${webos_preferences} variable is used, but this variable was wrong.
${webos_preferencesdir} should be used to add the /var/preferences
properly.

:Detailed Notes:

:Testing Performed:
Confirmed that /var/preferences was created with mode 755.

:QA Notes:

:Issues Addressed:
[GF-39768] Is it safe for /var/preferences to be world-writable?
[GF-53532] CCC: base-files=webos8

Open-webOS-DCO-1.0-Signed-off-by: Seonho Park <seonho.park@lge.com>

Change-Id: I4fb6eb71198a55a8ebb10d11e9d540ba0a24027a
Reviewed-on: https://g2g.palm.com/4084
Reviewed-by: DCO Verification
Build: Seonho Park <seonho.park@lge.com>
Reviewed-by: Seonho Park <seonho.park@lge.com>
Tested-by: Seonho Park <seonho.park@lge.com>
Reviewed-by: Build Verification
Reviewed-by: Martin Jansa <Martin.Jansa@lge.com>
Reviewed-by: Earnest Son <earnest.son@lge.com>
Reviewed-by: Joungyong Choi <joungyong.choi@lge.com>
Tested-by: Joungyong Choi <joungyong.choi@lge.com>