Add option to specify xmlRpcPassword value using standard input or a file

[gpoppino]

The password of a long running inter-server-sync process that uses the --xmlRpcPassword parameter can be seen with the ps command on Linux.

Provide an option to read the password from standard input or from a file, so that the password is kept secret.

[rjmateus]

@admd @thesp0nge for awareness

[thesp0nge]

Which is the password are we talking about?

[rjmateus]

The password that can be passed is used to connect the XML-RPC API, and will call a method to synch the configuration channels to the server file system