python3: KeyError to use format

Changes KeyError signatures to use `format` instead of `%`

partial: https://github.com/vmware/pyvmomi/issues/55
Merge pull request #96 from hartsock/issue/55

python3: KeyError message string changed to use format
testing: demonstrates basic container views

This test attempts to reproduce a bug report using
the code currently in `master`. The issue does not
appear to occur on the development branch.

closes: https://github.com/vmware/pyvmomi/issues/50
Merge pull request #99 from hartsock/issues/50

testing: demonstrates basic container views