Doc and test cert apis

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

doc,test,tls

Description of change

• doc,test: tls .ca option supports multi-PEM files
• test: tls cert chain completion scenarios
• doc: use correct tls certificate property name
• test: check tls server verification with addCACert
• test: move common tls connect setup into fixtures