Reuse xnat session from `xnat.connect()` outside `sync_xnatpy` function

[kcho]

The current design of modules including lochness.xnat requires API login for each subject. This adds a short, but significant delay to the dataflow. lochness.xnat.sync_xnatpy is a good example.

lochness/lochness/xnat/__init__.py

Lines 240 to 242 in 9eb6e1b

	session = xnat.connect(keyring['URL'],
	keyring['USERNAME'],
	keyring['PASSWORD'])

Is there a (simple) way to keep the connection, in this case the session variable, to be reused for other subjects instead of logging in again?