Verbose logging on error

* Create rest logger instance only once.
* If the token does not seams special it is omitted.
* The log level setting in tempest.conf has limitations in
  configuring log level, so it is removed for now.
* No extra logging on error in any different log level.

Bug: #1089846

Change-Id: Ibd664520e81e072ea1040c47d0aeef4980903118
Merge "Verbose logging on error"