fix regex for cleaning old logs with ipcluster

it still had the 'z' suffix from ages and ages ago, so no files would ever match.

closes #4810
Error in Session.send_raw()

Addresses issue ipython/ipython/#4839.
Added test_send_raw() for issue #4839, see pull request 4840
Removed debug prints
adjustments to notebook app logging

Mainly add a log_request function (from nbviewer) for formatting tornado access logs.

Relevant effects:

- demote successful access logs to DEBUG
- demote kernel connect messages to DEBUG

which reduces the noise at INFO-level (default)
Merge pull request #4840 from dsblank/master

Error in Session.send_raw()
Merge pull request #4844 from minrk/tornado-logs

adjustments to notebook app logging

Mainly add a log_request function (from nbviewer) for formatting tornado access logs.

Relevant effects:

demote successful access logs to DEBUG
demote kernel connect messages to DEBUG
which reduces the noise at INFO-level (default)
Merge pull request #4820 from minrk/super-old-z

fix regex for cleaning old logs with ipcluster