cve-check: allow feed choice

cve-check: allow feed choice

Allow choice of one of three feeds and update task dependencies
accordingly. All feeds contain data from NVD and are stored in
different files.

Set the NVD_DB_VERSION variable to choose feed:
NVD2 (default) - the NVD feed with API version 2
NVD1 - the NVD JSON feed (deprecated)
FKIE - the FKIE-CAD feed reconstruction

In case of malformed database feed name, we default to NVD2 and show
an error.

Signed-off-by: Marta Rybczynska <marta.rybczynska@ygreky.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>