Version 1.7.2 - fixes a bug in JSON-encoding.
Fix ValueError when handling bulk_delete response.

When performing a bulk delete request, `ValueError: needs more than 1 value to unpack` is raised on line 1552, because it appears one of the lines in the response is a blank line with spaces in it.  Such a value for `resp_line` will, of course, pass the `if not resp_line` precondition but fail on `resp_key, val = resp_line.split(":", 1)`.
Merge branch 'master' into working
Changed to cleaner condition.
Merge branch 'patch-1' of github.com:asavoy/pyrax into asavoy-patch-1

GitHub #335