[Tizen] Fix for build break caused by new version of NSS

Chromium requires new version of NSS => 3.14.3, while Tizen
has NSS version 3.12.9.This patch switches xwalk to use
openssl, until Tizen gets upgraded version of nss package.
Merge pull request #857 from alexshalamov/fix_nss_break_use_openssl

[Tizen] Fix for build break caused by new version of NSS
Bump version to 2.31.15.0