relocate generic actions out of execute action

These are intended to not be coupled to RunOnces. Decoupling will be done in
a later commit.
rename files for consistency
make Performer interface synchronous
RunOnceHandler tests happy path, instead of types
decouple generic actions from RunOnce

Introduce lazy action runner; given a thunk, it'll invoke it when being
Performed to generate its actions. This allows the execute action to be
created before we know the handle/etc. of the RunOnce.
Merge pull request #3 from cloudfoundry-incubator/action-runner-cleanup

Action runner cleanup