Fix APIError for requests 1.1

requests 1.1, which is what's available on CentOS 6, doesn't support
passing the response code as a keyword argument.  It can be set after
the fact on both requests 1.1 and 1.2.

Docker-DCO-1.1-Signed-off-by: Chris St. Pierre <chris.a.st.pierre@gmail.com> (github: stpierre)
Merge pull request #165 from stpierre/fix-http-error

Fix APIError for requests 1.1