Handle JSON hooks that just close the file/exit and fix some other errors

JSON hooks might disappear and the common idiom to work around hooks
disappearing is to check for the hook in the shell snippet that is
in the apt.conf file and if it does not exist, do nothing. This caused
APT to fail however, expecting it to acknowledge the handshake.
Ignoring ECONNRESET on handshakes solves the problem.

The error case, and the other error cases also did not stop execution
of the hook, causing more errors to pile up. Fix this by directly going
to the closing part of the code.

LP: #1776218
(cherry picked from commit 1d53cffad22c92645090e0e6ddde31fe4f7c3b05)

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