make libssh module default to the "new" libssh config by default

Summary:

• rename module from LibSSH to libssh so casing is consistent with config
• module now quietly attempts to find libssh by config and returns if found
• if it was not found we'll fall back to manual lookup
• adjust actual FOUND variable use for correct case
• fix package case in properties set up (this is case sensitive)

this is singularly necessary because the config file is not correctly
packaged in ubuntu 18.04 (LTS)

https://bugs.launchpad.net/ubuntu/+source/libssh/+bug/1800135/comments/2

This reverts 3b1fd6bd8866da2dadd33705af53613236503efc.

BUG: 400291

Test Plan: builds in ubuntu docker container and with a system that has a proper config

Reviewers: broulik, asn

Reviewed By: broulik

Subscribers: kde-frameworks-devel, kfm-devel

Tags: Dolphin, Frameworks

Differential Revision: https://phabricator.kde.org/D16529