UBUNTU: [Debian] Support custom and lts kernels in printchanges/insertchanges

UBUNTU: [Debian] Support custom and lts kernels in printchanges/insertchanges

Ignore: yes

Currently printchanges/insertchanges do not work for custom kernels
because commit messages for each release follow the format
"UBUNTU: Ubuntu-${flavour}-${prev_fullver}" instead of
"UBUNTU: Ubuntu-${prev_fullver}". Also, for the first release, the
previous version in the changelog does not match the version in the
previous release commit.

This patch makes the base commit selection more flexible, allowing
commit messages in the format "UBUNTU: Ubuntu-*${prev_fullver}" and it
fallbacks to the latest release commit when a exact match is not found
in order to support the custom kernels in their initial releases.

Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>