fix(cert-create): change WARN to VERBOSE

SAVE_KEYS is set to '0' by default, causing cert_create to
show the 'Key filename not specified' message on each run
even though this is perfectly normal. Show the message only
in the VERBOSE log level.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Change-Id: I472cdec2670055ab0edd99d172f79d01ad575972
1 file changed