certificate_authority: unique_subject = no

"openssl ca" is keeping track of all generated certificates in its DB.
If we try to regenerate a certificate that was already generated,
openssl ca fails with :

ERROR:There is already a certificate for /C=XX/ST=(State,)/O=Company/CN=ca-shellinabox/emailAddress=xx@example.com

Changing "unique_subject" to no removes this ERROR.

/reviewed-on !556

slapos/recipe/certificate_authority/template/openssl.cnf.ca.in

@@ -43,7 +43,7 @@ dir		= %(working_directory)s		# Where everything is kept
 certs		= $dir/certs		# Where the issued certs are kept
 crl_dir		= $dir/crl		# Where the issued crl are kept
 database	= $dir/index.txt	# database index file.
-#unique_subject	= no			# Set to 'no' to allow creation of
+unique_subject	= no			# Set to 'no' to allow creation of
 					# several ctificates with same subject.
 new_certs_dir	= $dir/newcerts		# default place for new certs.