Unittests are failing with urllib3>1.26

[matusvalo]

Unittests are failing with error:

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <botocore.awsrequest.AWSHTTPConnection object at 0x7f9c856d7278>

header = 'Host', values = (b'169.254.169.254',)

    def putheader(self, header, *values):

        """"""

>       if SKIP_HEADER not in values:

E       BytesWarning: Comparison between bytes and string

.tox/3.7-linux-unit/lib/python3.7/site-packages/urllib3/connection.py:218: BytesWarning

It seems that the issue was introduced by:
urllib3/urllib3#2018

[thedrow]

We probably need an issue to support the newer versions...