Update coverage config

Author: bridadan

legacy/mbed-greentea/.coveragerc

@@ -1,19 +1,3 @@
 [run]
-include =
-    mbed_greentea/*
-
-[report]
-exclude_lines =
-    class GreenteaHook.*
-    def __repr__
-    def run_test_thread.*
-    except ImportError.*
-    except IOError.*
-    except OSError.*
-    except UnicodeDecodeError.*
-    gt_logger.*
-    if __name__ == .__main__.:
-    main().*
-    pragma: no cover
-    raise AssertionError
-    raise NotImplementedError
+source =
+    mbed_greentea