IGuest.create_session() fails with an empty password

[sethmlarson]

ENVIRONMENT

• Operating System: Any
• Python version: Any
• VirtualBox version: 5.1.x
• VirtualBox SDK version: 5.1.x
• pyvbox version: 1.0.0
• Happens in latest master branch?

SUMMARY

When creating an IGuestSession via IGuest.create_session() if a zero-length password is given an error will be raised. This was found originally by @aGGeRReS in issue #47. Proposed fix is to throw a better error message if this error is caught and an empty password is used.

STEPS TO REPRODUCE

vbox = virtualbox.VirtualBox()
session = virtualbox.Session()
vm = vbox.find_machine('Windows7')
vm.launch_vm_process(session, 'gui', '').wait_for_completion()

session = vm.create_session()
gs = session.console.guest.create_session('win7', '')

EXPECTED RESULTS

To login to the Guest Session with an empty password.

ACTUAL RESULTS

Raises an exception

gs = session.console.guest.create_session('win7', '')
File "/usr/local/lib/python2.7/dist-packages/virtualbox/library_ext/guest.py", line 24, in create_session
raise SystemError("GuestSession failed to start")
SystemError: GuestSession failed to start