optimize engine cache checker (projecteru2#539)

optimize engine cache checker (projecteru2#539)

try to make client when node is not available (projecteru2#538)

fix map concurrent write issue (projecteru2#530)

build binary for darwin (projecteru2#522)

add validation for AddNode (projecteru2#515)

fix: change signature of build (projecteru2#512)

implement imagePush and buildRefs (projecteru2#509)

return imgID in buildFromExist

set the unreachable nodes as unavailable (projecteru2#508)

Implement lambda related functions (projecteru2#500)

* implement wait

* implement log

* implement attach

* modify create

* refactor log