Fix broken homebrew installation in Ansible 1.8.x

Ansible 1.8.x includes this git module change https://github.com/ansible/ansible-modules-core/commit/0257cb120194403012eb553ce2f5b39346b0a7e4#diff-feb3a901687766220b4e9dee0d263157R547 which means that 'update' option set to 'no' results in only ls-remote instead of clone.
The above caused ansible-role-homebrew to only ls-remote and hence the symlink task will fail because the brew binary won't exist.

Another change I made was the default homebrew_install_path to /usr/local/homebrew. With /usr/local, it creates many files in homebrew source polluting /usr/local, possibly conflicting with pre-existing paths . When users want to uninstall, they have to be careful to delete homebrew files only.
Using /usr/local/homebrew is cleaner and more consistent with plenty other installations like qt, clam, go, meteor, etc.