(CFACT-58) Make blkid and openssl dependencies optional.

This commit makes blkid and openssl an optional build-time dependency.

If blkid isn't installed at build time for Linux, the partitions fact will be unavailable.

If openssl isn't install at build time, the SSH fingerprinting facts will be unavailable.

The dependencies can also be disabled using "-DWITHOUT_OPENSSL=1" and "-DWITHOUT_BLKD=1"
when configuring cmake.