Enable F821 check: undefined name 'name'

Enable F821 and fix usage of undefined variables.

In glance/common/client.py in BaseClient class image_iterator()
function returns instances of unexisting classes:
- SendFileIterator
- ImageBodyIterator
Since we have not these classes functionality now, we will use
utils.chunkreadable() function instead.

Delete image_iterator() function.

Change-Id: Ie1a8c66e5df2836e6e9aadfb1013d69fc6f710e6
Merge "Enable F821 check: undefined name 'name'"