Setup distributed lock for testing

Needs ilock from pypi to work, will do nothing if not present.

oggm/tests/conftest.py

@@ -0,0 +1,20 @@
+import pytest
+import logging
+import multiprocessing as mp
+from oggm import cfg, utils
+import pickle
+
+logger = logging.getLogger(__name__)
+
+def pytest_configure(config):
+    logger.info("in outer pytest_configure")
+    if config.pluginmanager.hasplugin('xdist'):
+        logger.info("has xdist")
+        try:
+            from ilock import ILock
+            utils.lock = ILock("oggm_download_lock")
+            logger.info("ilock locking setup successfully")
+        except:
+            logger.info("could not setup ilock locking")
+
+logger.info("conftest loaded")