Add libcloud API unit tests for CentOS, CernVM, Ubuntu VM (#7)

src/main/python/stratuslab_usecases/api/BasicVmLifecycleTestBase.py: Allow for timeout and sleepInterval specification, use same image as for CLI test, verify return value of functions
src/main/python/stratuslab_usecases/api/libcloud-drivers-use-cases.ini: Add the new tests
src/main/python/stratuslab_usecases/api/testBasicVmLifecycleCentOS.py: Add test
src/main/python/stratuslab_usecases/api/testBasicVmLifecycleCernVM.py: idem
src/main/python/stratuslab_usecases/api/testBasicVmLifecycleUbuntu.py: idem
src/main/scripts/bin/stratus-run-usecases: Add the new tests, use same verbositylevel for tests
Merge more libcloud API tests