Add support for canceling goals

[cdupuis]

This adds support for canceling goals:

export const cancel = new Cancel({ goals: [autofix, build, dockerBuild, publish] });

This goal when added to a goal set will cancel all pending or in process auto fix, build, docker build and publish goal instances on the current goal's push.before.sha of the same branch.

Which goals should be canceled can you be defined with the goalFilter on CancelOptions:

/**
 * Options to configure the Cancel goal
 */
export interface CancelOptions {

    /**
     * Goals that should be canceled if they are in a state that allows cancellation
     */
    goals: Array<Goal | Goals>;

    /**
     * Filter goals to cancel based on goalSet or state
     * @param goalSet
     */
    goalFilter?: (goal: SdmGoalEvent) => boolean;
}

fixes #571

[ddgenome]

Looks good. One question about a null check.

[lievendoclo]

OK

[atomist-bot]

Pull request auto merged by Atomist.

• 2 approved reviews by @ddgenome, @lievendoclo
• 2 successful checks

[atomist:generated] [auto-merge:on-approve]