cmake: fix build on Ubuntu 14.04

Fixed a syntax error with setting cache variables (The type and
docstring were missing), resulting in build errors.  Quoted the
CURL_CA_PATH and CURL_CA_BUNDLE otherwise the path was written without
quotes in C code, resulting in build errors.

Closes #1503

Signed-off-by: Akhil <akhil.kedia@samsung.com>