Avoid propigating nonzero exit status of any command called by etckeeper out to the caller. This is to avoid making apt give up because git is misconfigured and cannot commit, or similar. Closes: #760011

I absoltely do not want etckeeper to dive into the rats nest of making git
be able to commit reliably. git commit has about a dozen failure modes, and
it's up to the admin to avoid breaking their system by not giving it a
hostname, or writing a broken ~/.gitconfig, or not giving uid 0 a user
name, etc.

I considered making only apt.conf's etckeeper calls be guarded with ||
true, but this would also need to be done for the other package managers
that can call etckeeper. And it's better to let etckeeper
indicate which script failed, rather than seeing an error message and apt
continuing without an indication of why git commit was being called then.
prep release
better status output
Revert "Avoid propigating nonzero exit status of any command called by etckeeper out to the caller. This is to avoid making apt give up because git is misconfigured and cannot commit, or similar. Closes: #760011"

This reverts commit 1b70e83dddcafbcbea84fc55a6396e4876a9a0c4.

This approach breaks the AVOID_COMMIT_BEFORE_INSTALL feature.
Use debconf for prompting when post-install commit fails, as was already done for pre-install commit. This avoids propigating errors to apt when eg, git is misconfigured and cannot commit. Closes: #760011
let's not use debconf to display a possibly minor warning
prep release