Update mixer used to work with multiple repos

[ashleshaAtrey]

You can use "mixer repo add " command to add new repos.
Add the repo url with file:// , http or https protocol

You can remove the "clear" repo from repo list if not needed using "mixer repo remove " command.
But "local" repo is auto added if removed with default url file:///local-yum.

You can set priorities to repos by editing ".yum-mix.conf file". We don't have mixer commands to set priority yet.

[ashleshaAtrey]

If protocol used is file://, the path should be absolute and it should point to where the rpms are stored with repodata present in that directory.