Add version parameter to adapter.

The version parameter was left out of adapter previously because setting
a version number triggers discovery and I felt that it was not ready for
the other services.

However if it isn't set then it won't be used and we may as well
implement it here once rather than have the individual services that do
support it override it themselves.

Change-Id: I707380a01175dc19b59de32cbb8fd2bb123d7335
Merge "Add version parameter to adapter."