bintree: use urllib provided attributes for hostname, user and password

[parona-source]

In addition to simplifying it also solves an issue with parsing raw ipv6 addresses.

Bug: https://bugs.gentoo.org/921400

>>> test = urlparse("ssh://[::1]/var/cache/binpkgs")
>>> test.netloc
'[::1]'
>>> test.hostname
'::1'
>>> test = urlparse("ssh://[::1]:23/var/cache/binpkgs")
>>> test.netloc
'[::1]:23'
>>> test.hostname
'::1'
>>> test = urlparse("ssh://test@[fe80::1ff:fe23:4567:890a]:23/var/cache/binpkgs")
>>> test.netloc
'test@[fe80::1ff:fe23:4567:890a]:23'
>>> test.hostname
'fe80::1ff:fe23:4567:890a'
>>> test.port
23
>>> test = urlparse("ssh://test:password@[fe80::1ff:fe23:4567:890a]:23/var/cache/binpkgs")
>>> test.netloc
'test:password@[fe80::1ff:fe23:4567:890a]:23'
>>> test.hostname
'fe80::1ff:fe23:4567:890a'
>>> test.port
23
>>> test.username
'test'
>>> test.password
'password'

[mgorny]

LGTM but I've no clue why it was done like that.