As reported in #9132, if one sets `http_proxy=myproxy:8080` the URL
gets parsed to scheme=myproxy and host=nil. This results in a
NullPointerException.
To solve it, we check that the URL is valid as HTTP/HTTPs and raise a
slightly better error message.
Fixes#9132.
Fixes#9230
On some Linux system like debian, the `HTTP_PROXY` are set to an empty
string and was causing the plugin manager to raise an exception. We now
strip the string and check if it is empty before trying to configure the
proxies.
Fixes: #7045Fixes#7065
Logstash's plugin manager will now follow proxy configuration from the environment.
If you configure `http_proxy` and `https_proxy`, the manager will now use theses information for all the ruby http
connection and will also pass that information down to maven.
Fixes: #6619, #6528Fixes#6825
