Clean up logging levels

The following logging levels are set according to the combination of
--verbose, --quiet and --debug options:

verbose_level   logging level       options
0               --quiet             ERROR
1               (none)              WARNING
2               --verbose           INFO
3+              --verbose --verbose DEBUG
                or --debug

Logging levels for the requests and iso8601 modules are forced to ERROR
unless --debug is given.

Change-Id: Ide2233b3316471d279260fb1e7255a6ca2072023
Merge branch 'server-image-create-fix' into dt-test
Merge branch 'image-set-fix' into dt-test
Merge branch 'fix-logging' into dt-test
Merge branch 'new-session' into dt-test
Merge branch 'identity-ec2-tests' into dt-test