feat/get_oldest_file's_timestamp

@haufs @karnem a modification to get_dir_creation_date() function in cal_tools for returning the timestamp of the oldest .h5 file in the run directory. That is instead of returning the timestamp for the whole directory.

cal_tools/cal_tools/tools.py

@@ -425,16 +425,23 @@ def get_notebook_name():
         return environ.get("CAL_NOTEBOOK_NAME", "Unknown Notebook")
 
 
-def get_dir_creation_date(directory, run):
+def get_dir_creation_date(directory, run, tsdir=False):
     """
-    Return modification time of [directory]/[run]04
+    Return modification time of oldest file.h5 in [directory]/[run]04
 
     :param directory: path to directory which contains runs
     :param run: run number
+    :param tsdir: to get modification time of [directory]/[run]04.
     :return: (datetime) modification time
     """
-    creation_time = stat("{}/r{:04d}".format(directory, run)).st_mtime
-    creation_time = datetime.datetime.fromtimestamp(creation_time)
+    if tsdir:
+        creation_time = stat("{}/r{:04d}".format(directory, run)).st_mtime
+    else:
+        rfiles = glob("{}/r{:04d}/*.h5".format(directory, run))
+        rfiles.sort(key=path.getmtime)
+        creation_time = stat(rfiles[0]).st_mtime
+
+    creation_time = datetime.datetime.fromtimestamp(creation_time)     
     return creation_time