debian: Don't overwrite changelog when OBS bumps the version

OBS adds an additional version suffix at the beginning of the build in
debian/changelog. This breaks the Ubuntu flow where all real changes go
into debian.master/changelog. Likewise, the version detection in the
rules (unlike the debian packaging tools) read debian.master/changelog.
We need to preserve the OBS version, so keep the two files in sync
during clean.

[endlessm/eos-shell#2600]
debian: Rename abi directory to current endless release

With the previous hack to keep the two changelogs in sync, the debian
packaging will now regard the version OBS generates correctly. That
means that when OBS is running, the previous version will be endlessX
and the current version will be endlessXbemY.

In that case, we need to change the module ABI directory name (or add a
new module directory) every time we do a release so that the the ABI
checker will find the "previous" version file.

[endlessm/eos-shell#2600]
Merge pull request #1 from endlessm/shell/2600

Shell/2600