Rename test_testcase_base to test_testcase

It follows "Rename testcase_base to testcase" [1]

[1] https://gerrit.opnfv.org/gerrit/#/c/31879/

Change-Id: I54bb62a37bdab842f433790688128a459b0ac78c
Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>

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