static-checks: Use proper ref branch when collecting commits to test

Use the actual branch specified in the CI run, instead of hardcoded
master/integration.

Addresses https://linaro.atlassian.net/browse/TFC-636

Cherry-pick: Fixed conflicts while applying to lts-v2.10 branch.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: Ic0fd0677978f226626d567108f17ccb864aa8095
6 files changed