Fix lf-release-jobs

Fix lf-release-jobs

Add -m to deal with merge commits.

-m
By default, git diff-tree --stdin does not show differences
for merge commits. With this flag, it shows differences
to that commit from all of its parents.

Refactor packagecloud release/merge parameters and add distribution_type
as environmental variable.
Remove distribution_type from pypi and packagecloud schema.
Add variable values for packagecloud in release-job.sh.

ISSUE-ID: RELENG-2567
Signed-off-by: Houa Yang <hyang@contractor.linuxfoundation.org>
Change-Id: I4bf718874b754bd24c03e22a9184e0b1566075e9