Fixed usage of WebUserAgent throught proxies for HTTPS urls.

LWP has a long-standing issue that it can not access HTTPS urls using
a proxy server.
See https://rt.cpan.org/Ticket/Display.html?id=1894

The workaround is to force usage of Net::SSL, set $ENV{HTTPS_PROXY} and
also turn off hostname verification. This last bit because Crypt::SSLeay
which provides Net::SSL does not implement hostname verification yet
(plus, OTRS does not do hostname verification either).

Fixes bug#9541 - Package manager cannot use https proxy.
http://bugs.otrs.org/show_bug.cgi?id=9541