Rename test_pytest_suite_runner.py to test_unit.py

It conforms with [1].

[1] https://gerrit.opnfv.org/gerrit/#/c/35211/

Change-Id: Ife7a161970997cf6cd74e86c343d4879f87b5cf4
Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

diff --git a/functest/tests/unit/core/test_pytest_suite_runner.py b/functest/tests/unit/core/test_unit.py
similarity index 100%
rename from functest/tests/unit/core/test_pytest_suite_runner.py
rename to functest/tests/unit/core/test_unit.py