New option to request a repo without an initial commit
    
    A new option --no-initial-commit is added to request a repository
    without an initial commit. When specified, a new item is added to
    ticket, which looks like
    
    {
     "action": "new_repo",
     "branch": "master",
     ...
     "initial_commit": false
    }
    
    initial_commit with value false indicates not create the initial
    commit.
    
    Fixes #215
    
    Signed-off-by: Chenxiong Qi <cqi@redhat.com>