This updates the ClearCase unit tests to build a ClearCaseClient in

each test where it's needed, rather than in setUp(). This is in

prepration for new tests that will need to handle client construction

differently.
Tests are no longer skipped if cleartool is missing. These tests mock

all the cleartool invocations, with the exception of the initial

cleartool check and fetching host properties. With these set up with

spies, we no longer need to worry about whether cleartool is

installed.

ClearCase unit tests pass.