Looking into this a little more the error your getting "unable to find valid certification path to requested target" means the SSL certificate needed to connect could not be found in the truststore that the workflow engine is using.
Do you know what java truststore you imported the certificate into it?
This is usually the steps I take for importing the certificate:
# Copy the certificate into the directory Java_home\Jre\Lib\Security
# Change your directory to Java_home\Jre\Lib\Security>
# Import the certificate to a trust store.
keytool -import -alias ca -file somecert.cer -keystore cacerts -storepass changeit [Return]
Trust this certificate: [Yes]
If it's a custom truststore, you could update the workflow engine service parameter and add it there:
Edit the ImagePath to something like:
"C:\Program Files\Commvault\ContentStore\Base\CVJavaService.exe" -Djavax.net.ssl.trustStore="c:\path\mycustomtruststore" -jar "C:\Program Files\Commvault\ContentStore\WFEngine\workflowEngine.jar" -serviceName CVJavaWorkflow(Instance001) jre 1.8 -program Workflow -vm Instance001