CI scripts for the release process

It provides method to build, package and deploy artifacts, as
well as constructing announcement mails:
   - bazel_build build bazel with the good label, execute the tests,
     build the packages and copy the artifacts into a release directory.
   - bazel_release deploy the relase to GCS and Github and send an
     announcement mail.

--
Change-Id: I68f5a600c0718fac5fa12423d1cb8e0cc86728b5
Reviewed-on: https://bazel-review.googlesource.com/#/c/1811
MOS_MIGRATED_REVID=100805636

scripts/ci/release_email.txt

diff --git a/scripts/ci/release_email.txt b/scripts/ci/release_email.txt
new file mode 100644
index 0000000..4b0cb01
--- /dev/null
+++ b/scripts/ci/release_email.txt
@@ -0,0 +1,11 @@
+bazel-discuss+release@googlegroups.com
+Bazel release %release_name%
+Bazel %release_name% is now available for general usage at:
+  %url%
+
+If you observe any regression, please report it to
+https://github.com/google/bazel/issues as soon as possible.
+
+The release notes for version %release_name% are:
+
+%relnotes%