[experiments] Fixed database indexing when running an experiment

The wrong path was used to generate the index.

Logging has also been improved.

beat/cmdline/experiments.py

@@ -153,15 +153,17 @@ def run_experiment(configuration, name, force, use_docker, use_local):
             return "%.2f gigabytes" % (s / gb)
         return "%.2f terabytes" % (s / tb)
 
-    def index_experiment_databases(prefix, experiment):
+    def index_experiment_databases(cache_path, experiment):
         for block_name, infos in experiment.datasets.items():
             view = infos['database'].view(infos['protocol'], infos['set'])
             filename = toPath(hashDataset(infos['database'].name,
                                           infos['protocol'],
                                           infos['set']),
                               suffix='.db')
-            if not os.path.exists(filename):
-                view.index(os.path.join(prefix, filename))
+            database_index_path = os.path.join(cache_path, filename)
+            if not os.path.exists(database_index_path):
+                logger.info("Index for database %s not found, building it", infos['database'].name)
+                view.index(database_index_path)
 
     dataformat_cache = {}
     database_cache = {}
@@ -182,7 +184,7 @@ def run_experiment(configuration, name, force, use_docker, use_local):
         os.makedirs(configuration.cache)
         logger.info("Created cache path `%s'", configuration.cache)
 
-    index_experiment_databases(configuration.path, experiment)
+    index_experiment_databases(configuration.cache, experiment)
 
     scheduled = experiment.setup()