[leasing] Bring leasing.py to Python3
[leasing] Bring leasing.py to Python3

Bug: skia:13009
Change-Id: Ia2445ebce0b2fde5369ce5fbfab36af8c759dfe1
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/514745
Reviewed-by: Erik Rose <042ad22d8352d59a3d816dac710aebe65456f16e@google.com>
Commit-Queue: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@google.com>
Commit-Queue: Erik Rose <042ad22d8352d59a3d816dac710aebe65456f16e@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot