service: Remove user management, use PAM auth

Remove user management and replace with username
Update service unit tests
Remove passlib dependency
Add Python PAM dependency
Change auth to use Python PAM
Service: Add support for multi-tennancy

Disable ensemble manager
Authenticate users with PAM
Change to forking web server
Set uid/gid in handler process
Refactor dashboard database connections
Cleanup netlogger python
Remove service schema admin and migrations
Disable service unit tests
Remove pegasus-service-admin from documentation