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'"
Fix RBD store to use READ_CHUNKSIZE

Change 4e0c563b8f3a5ced8f65fcca83d341a97729a5d4 was incomplete and
missed a variable in the rbd store.

This patch fixes the issue by using store.READ_CHUNKSIZE instead of
store.chunk_size

Change-Id: I2dc5b1514d3e86ec129c1fc88de096d98a64f806
Closes-Bug: #1352509