MODSIGN: do not send garbage to stderr when enabling modules signature

When compiling kernel with -jN (N > 1), all warning/error messages
printed while openssl is generating key pair may get mixed dots and
other symbols openssl sends to stderr. This patch makes sure openssl
logs go to default stdout.

Example of the garbage on stderr:

crypto/anubis.c:581: warning: ‘inter’ is used uninitialized in this function
Generating a 4096 bit RSA private key
.........
drivers/gpu/drm/i915/i915_gem_gtt.c: In function ‘gen6_ggtt_insert_entries’:
drivers/gpu/drm/i915/i915_gem_gtt.c:440: warning: ‘addr’ may be used uninitialized in this function
.net/mac80211/tx.c: In function ‘ieee80211_subif_start_xmit’:
net/mac80211/tx.c:1780: warning: ‘chanctx_conf’ may be used uninitialized in this function
..drivers/isdn/hardware/mISDN/hfcpci.c: In function ‘hfcpci_softirq’:
.....drivers/isdn/hardware/mISDN/hfcpci.c:2298: warning: ignoring return value of ‘driver_for_each_device’, declared with attribute warn_unused_result

Signed-off-by: David Cohen <david.a.cohen@intel.com>
Reviewed-by: mark gross <mark.gross@intel.com>
Acked-by: David Howells <dhowells@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>