bin/pwclient: accept alternate http_proxy forms

bin/pwclient: accept alternate http_proxy forms

The forms for http_proxy (and the likes) is not very well defined nor
documented in any authoritaive place. However, there are two common
forms:  http://host:port  or  http://host:port/

Currently, the code chokes on the latter (e.g. with
http_proxy=http://127.0.0.1:8080/ ):

    [...]
      File "/usr/lib/python2.7/httplib.py", line 792, in _get_hostport
        raise InvalidURL("nonnumeric port: '%s'" % host[i+1:])
    httplib.InvalidURL: nonnumeric port: '8080/'

Chop off any slash character in the port definition to accept the second
form. If there is no '/' in there, it still works.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Stephen Finucane <stephenfinucane@hotmail.com>