Change version conventions

Use a `.` instead of `-` for version numbers. This is due to
a conflict with pep440 that triggers once you have a long
enough version number. This may be a bug in `pip` but it is
not pragmatic to think we can have that fixed in the near-term.

Closes https://github.com/vmware/pyvmomi/issues/174
Merge pull request #175 from hartsock/v5.5.0.2014.1.1

Change version conventions