added base64 decoding of username and password

[tek0011]

The issue is when using username/password that the base64.b64encode function requires a bytes-like object, but it's receiving a string instead.

We can fix this by encoding the username and password string before passing it to base64.b64encode.

[theforeman-bot]

Can one of the admins verify this patch?

[sbernhard]

Can you please fix the indention, like in https://github.com/theforeman/smart_proxy_salt/pull/91/files#diff-7837e29df8da6b091fd69027c5e8a287cc646a6c06332cf9f9474821e92e3b36L56

[tek0011]

Im not sure the original file was correctly formatted. I have ran this through python linting, it should now be following pythons suggested formatting. This is following PEP 8, but I can remove the empty lines between comments and def's if you want.