omni: Fix the echo merge conflicts

 * Drop the deprecated --force-broken option. It's true by default

 * Use porcelain option to grep if there's an merge conflict
   https://git-scm.com/docs/git-status/2.0.5

 * Only abandon merge if one merge conflict is in progress.

Change-Id: I610d423ad17442f1b1eea3c83a4a18dfe523c7ad
3 files changed