Small fixes around variable usage

glance_http.py:
* We import the json module in all other files without a fall back
  the glance client should not be different
* The detailed message for the exceptions are generated, but not used.

image_client.py:
* 'time' package is a not used import.

container_client.py:
* 'marker' variable not in use.

test_absolute_limits.py:
* 'testtools' import not in use.

test_disk_config.py, test_server_personality.py:
* 'rand_name' imported, but not used.

Change-Id: I3f543d8d49c92d136f4cff07a776242329eb5ec4
Merge "Small fixes around variable usage"