Fix pattern parsing from <package>:<pattern> string

Split `<pattern>` argument into tests_dir glob and pattern glob as being found
in unittesting.json.

MyPackage:mytests/**/test*.py 
   => package=MyPackage, tests_dir=mytests/**, pattern=test.py

If no path is given, `tests_dir` from unittesting.json or default is used.

MyPackage:test*.py 
   => package=MyPackage, tests_dir=tests/, pattern=test.py

Author: deathaxe

unittesting/unit.py

@@ -56,7 +56,11 @@ def run(self, package=None, **kwargs):
         # parse input of form `<package>:<pattern>`
         parts = package.split(":", 1)
         if len(parts) == 2:
-            package, kwargs["pattern"] = parts
+            package, pattern = parts
+            tests_dir, pattern = os.path.split(pattern)
+            if tests_dir:
+                kwargs["tests_dir"] = tests_dir
+            kwargs["pattern"] = pattern
 
         # resolve real package name
         if package == "$package_name":