Fetch the partner ref. with fetch-and-push-partner tool

Extract the logic to fetch the partner ref. from merge-partner-on-aosp
to a new tool: fetch-and-push-partner that requires special credentials.

This patch makes sure the merge-partner-on-aosp tool now uses whatever
partner ref. exists in origin instead of retrieving a possibly updated
ref. before merging. This avoids confusion when pushing merge commits for
review: both local and remote repositories are starting from the same
branch states. Only the merge commits needs to be reviewed, not new patches
coming from upstream.

The fetch-and-push-partner tool fetches the partner security branch from
the related Google partner repository and pushes it to origin. The tool
should be run prior to running merge-partner-on-aosp.

Issue: ST-1156
Change-Id: Ic35250da68122c1c7e0b4a7a4c84b1f9de90c048
2 files changed
tree: df703869e1ec67d4a66bc49c086dd8f7e4cb50cc
  1. fetch-and-push-partner
  2. merge-partner-on-aosp
  3. ota_install