Fix variable typo of use_syslog in lib/tempest

TEMPEST_CONF is not set but used it. As a result the meaningless file
'DEFAULT' is created. So this commit fixes to use proper variable name.

Closes-bug: #1394969
Change-Id: If6e58f269319df3c4f71b4fc13aa855c63f7e3a3
Add tooz support from Oslo

Change-Id: I4ccf4bf08e10c0ba651f973aa62562af85ea0f19
Merge "Add tooz support from Oslo"
Merge "Fix variable typo of use_syslog in lib/tempest"