Error self signed certificate getting chain

I'm learning to use Gatling to test scenario

I've been doing with guide from documentation here http://ift.tt/1qizHWV

Because my to-be-tested scenario includes logging in with Google Account, it is rejected due to lack of certificate. I followed guidelines to generate a certificate

openssl genrsa -out rootCA.key 2048
openssl req -x509 -new -nodes -key rootCA.key -days 1 -out rootCA.pem
openssl x509 -outform der -in rootCA.pem -out gatlingCA.crt
openssl genrsa -out device.key 2048
openssl req -new -key device.key -out device.csr
openssl x509 -req -in device.csr -CA rootCA.pem -CAkey rootCA.key -CAcreateserial -out device.crt -days 1
openssl pkcs12 -export -in device.crt -inkey device.key -out server.p12 -name gatling -CAfile rootCA.pem -caname gatling -chain
keytool -importkeystore -deststorepass gatling -destkeypass gatling -destkeystore gatling-custom.jks  -srckeystore server.p12 -srcstoretype PKCS12 -srcstorepass gatling -alias gatling

But after this command

openssl pkcs12 -export -in device.crt -inkey device.key -out server.p12 -name gatling -CAfile rootCA.pem -caname gatling -chain

The terminal alerts an error: Error self signed certificate getting chain

What's next to do if I want to continue to create my scenario with user session, then use it to test?