CLI currently allows to set both the result and the description of a build:

set-build-description
Sets the description of a build
set-build-result
Sets the result of the current build. Works only if invoked from within a build.

Attached patch adds a command that allows to set the displayName in a similar way.

This is my first contribution to this and I don't think I've been able to do satisfying tests on this one. Pointers welcome.