oeqa: Refactor test skipping decorators to use the unittest result object

oeqa: Refactor test skipping decorators to use the unittest result object

In order to make the test skipping decorators independent of the oeTest object we rely on the unittest result object to construct skip, fail and error lists used by these decorators.
Created a new object getResults that analyses upper frames and retrieves the unittest result object instance, then return a list of failed, skipped and error tests.
Also removed the oetest import from decorators.py because it was no longer required.

(From OE-Core rev: 4d2d201158236bd4c72546cf8db88681ff921b11)

Signed-off-by: Lucian Musat <georgex.l.musat@intel.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>