Fix update tests that fail for package installs.

Software updates are checked for but never offered in package installs.
Perhaps _MaybeCheckForAndOfferSoftwareUpdate should be split into two
functions so the "check for" and "offer" parts can be tested
independently but this fixes the tests as-is.
Merge pull request #148 from marineam/fixpkgtests

Fix update tests that fail for package installs.