validiation_pool: log leader change when attempting transaction

BUG=chromium:618159
TEST=unit tests pass

Change-Id: I391da542830fbcdc911d13d82c9fdf475c290228
Reviewed-on: https://chromium-review.googlesource.com/350781
Reviewed-by: Xixuan Wu <xixuan@chromium.org>
Reviewed-by: Shawn N <shawnn@chromium.org>
Tested-by: Aviv Keshet <akeshet@chromium.org>
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>
1 file changed