Safely handle, when uri contains IPv6 link local with %zone index

[jjlogu]

Issue:

When URI contains IPv6 link local with zone index (Ex: fe80::726f:8a26:222a:2bf3%eth0), requote_uri encodes all % to %25. Because of it, requests.get was requesting different resource.

Screenshot:

I'm proposing to ignore domain part in utils.unquote_unreserved.

Actual Result

>>> requests.utils.requote_uri('http://[fe80::726f:8a26:222a:2bf3%eth0]:8080/a%20b/index.html')
'http://[fe80::726f:8a26:222a:2bf3%25eth0]:8080/a%2520b/index.html'

Expected Result

>>> requests.utils.requote_uri('http://[fe80::726f:8a26:222a:2bf3%eth0]:8080/a%20b/index.html')
'http://[fe80::726f:8a26:222a:2bf3%eth0]:8080/a%20b/index.html'

System Information

# python3 -m requests.help
{
  "chardet": {
    "version": "3.0.4"
  },
  "cryptography": {
    "version": "2.2.2"
  },
  "idna": {
    "version": "2.8"
  },
  "implementation": {
    "name": "CPython",
    "version": "3.5.2"
  },
  "platform": {
    "release": "4.4.71-UNRELEASED-v4-00050-g76f27ecf9a52",
    "system": "Linux"
  },
  "pyOpenSSL": {
    "openssl_version": "1000207f",
    "version": "18.0.0"
  },
  "requests": {
    "version": "2.22.0"
  },
  "system_ssl": {
    "version": "1000207f"
  },
  "urllib3": {
    "version": "1.24.1"
  },
  "using_pyopenssl": true
}