update_engine: Detect supported minor version from conf file.
If the delta minor version is not given as a command line argument, the
payload generator will look for the minor version in
etc/update_engine.conf in the old image.
BUG=chromium:455493
TEST=`FEATURES=test emerge-link update_engine`
CQ-DEPEND=CL:249956
Change-Id: I0f8e3f3c05432169770f2e8e283e8f1fb363def3
Reviewed-on: https://chromium-review.googlesource.com/249955
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Allie Wood <alliewood@chromium.org>
Tested-by: Allie Wood <alliewood@chromium.org>
diff --git a/update_engine.conf b/update_engine.conf
new file mode 100644
index 0000000..ff69eb8
--- /dev/null
+++ b/update_engine.conf
@@ -0,0 +1 @@
+PAYLOAD_MINOR_VERSION=1