1. Optional arguement "--set-name" was renamed into "--set" for
consistency. See `rally verify start`.
2. The @envutils.with_default_deployment decorator was added to
the import_results method.
3. When we import some results and don't specify set name for tests,
in the verification table set name for these tests will be specified
as None. So the default value of the "set_name" parameter was changed
from None to "" to avoid this issue.
Change-Id: Icd6659f1a78c6a426c50c67cc31b7cd85f9fbd11
178e98958a