Fix case of incorrect status when test was skipped in setup.

When some test was skipped in the setup, RP wrongly identified its
status, by assigning to it the status of the last non-skipped test.

Test to reproduce:

"""
import pytest

@pytest.fixture
def skip_in_setup():
    pytest.skip()

def test_that_fails():
    assert False

@pytest.mark.usefixtures("skip_in_setup")
def test_skip_in_setup(self):
    pass
"""

In this example the first test fails and the second is skipped.
RP identified both as failures.

Author: KKoukiou

pytest_reportportal/listener.py

@@ -46,6 +46,7 @@ def pytest_runtest_makereport(self):
             )
 
         if report.when == 'setup':
+            self.result = None
             if report.failed:
                 # This happens for example when a fixture fails to run
                 # causing the test to error