Replace "LOG.exception(_" with "LOG.exception(_LE"
Replace "LOG.exception(_" with "LOG.exception(_LE"

Follow http://docs.openstack.org/developer/oslo.i18n/guidelines.html:
If a common message is not being used, they should each betreated
separately with respect to choosing a marker function.So this patch
is to fix it.

Change-Id: I07945d82320d9faf6dc452d49722af610330b441
Closes-Bug: #1600788

openstack/oslo.log