fix(cmd-api-server): shutdown hook was not waiting for promises

[petermetz]

1. The library we use for having async functions handle resource deallocation
   was not being used correctly by the API server.
2. The library only supports callback style asynchronous code and the API
   server assumed that it could return a promise from the shutdown hooks which
   lead to the problem that our shutdown hooks were not being awaited for.

Signed-off-by: Peter Somogyvari [email protected]

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A Must Read for Beginners
For rebasing and squashing, here's a must read guide for beginners.

[jagpreetsinghsasan]

LGTM