fix selfmon related known issues

Revert "Fix issue projecteru2#328 and some improvements. (projecteru2…

…#459)" (projecteru2#461)

This reverts commit 49dac53.

Fix issue projecteru2#328 and some improvements. (projecteru2#459)

* 1.Fix issue 328 by returning error.
2.Remove named return for better code readability.
3.Rename variable name colliding with import name.

* 1.Add ErrFunctionNotImplemented to handle error.
2.Add space between // and comments

* Add comment for exported function.

Co-authored-by: Jiabao Gu <[email protected]>

deal with extremely small resource rate (projecteru2#456)

make batchupdate idempotent (projecteru2#444)

allow replace not to decr processing key (projecteru2#442)

should only revoke when we don't use the lease

Enable eru core to make use of eru systemd runtime (projecteru2#418)

* use docker systemd engine to replace ssh engine

* refactor systemd engine

Co-authored-by: nyanpassu <[email protected]>
Co-authored-by: CMGS <[email protected]>

test needs a context as first parameter

revert to context.TODO