Git-upstream-import log (truncated past the point of previous-merge-point detection):

(git-upstream-latest) 2016-12-02.14:11 desbonne@kilcolgan2:~/tmp/neutron$ git-upstream --version
git-upstream 0.12.1
(git-upstream-latest) 2016-12-02.14:13 desbonne@kilcolgan2:~/tmp/neutron$ script -f git-upstream-import.log -c 'git-upstream -vvv import --import-branch hp/import/desbonne --into hp/prerelease/mitaka stable/mitaka'
Script started, file is git-upstream-import.log
Searching for previous import
Searching for most recent merge base with upstream branches
Upstream refs:
    stable/mitaka

Construct list of upstream revs to search:
    git rev-list --min-parents=1 --no-walk \
        stable/mitaka

Retrieve minimal list of revs to check with merge-base by excluding
revisions that are in the reachable from others in the list:
    git rev-list \
        c86f1ab75a97c4ea23c2533bc1d8d2b7baaae037 \
        --not \
        fe14343fabc21341f630d8bfd4dfce1b98524508

Running merge-base against each found upstream revision and target
    git merge-base hp/prerelease/mitaka ${upstream_rev}

Order the possible merge-base commits in descendent order, to
find the most recent one used irrespective of date:
    git rev-list --topo-order --max-count=1 --no-walk \
        0bc12bc4b3dd22cb1bcd34c3ff54225f14abe491

Most recent merge-base commit is: '0bc12bc4b3dd22cb1bcd34c3ff54225f14abe491'
Searching for previous merges that exclude one side of the history
since the last import.
    git rev-list --ancestry-path --merges 0bc12bc4b3dd22cb1bcd34c3ff54225f14abe491..hp/prerelease/mitaka

previous upstream: 0bc12bc4b3dd22cb1bcd34c3ff54225f14abe491
merge-base: 0bc12bc4b3dd22cb1bcd34c3ff54225f14abe491
parent: f716d76df03d080651a41c5e5bcbd72dec8744d3

previous upstream: 0bc12bc4b3dd22cb1bcd34c3ff54225f14abe491
merge-base: 0bc12bc4b3dd22cb1bcd34c3ff54225f14abe491
parent: a086cc5466e759843cc5a4002fb0500ceb5982e0

previous upstream: 0bc12bc4b3dd22cb1bcd34c3ff54225f14abe491
merge-base: 0bc12bc4b3dd22cb1bcd34c3ff54225f14abe491
parent: 43b9d0d734ca1736e040f76193b51f6ba69f544b

previous upstream: 0bc12bc4b3dd22cb1bcd34c3ff54225f14abe491
merge-base: 0bc12bc4b3dd22cb1bcd34c3ff54225f14abe491
parent: 903173e1ac39099eca5cac69b6af8063f993b430

previous upstream: 0bc12bc4b3dd22cb1bcd34c3ff54225f14abe491
merge-base: 0bc12bc4b3dd22cb1bcd34c3ff54225f14abe491
parent: 9c997bdf1c3099ae5e29b87ba506aaf532e7a2ab

previous upstream: 0bc12bc4b3dd22cb1bcd34c3ff54225f14abe491
merge-base: 0bc12bc4b3dd22cb1bcd34c3ff54225f14abe491
parent: c255028efdcf680d18d9bd7d03e9e52a55f0ed22

previous upstream: 0bc12bc4b3dd22cb1bcd34c3ff54225f14abe491
merge-base: 0bc12bc4b3dd22cb1bcd34c3ff54225f14abe491
parent: bf60247966cab6e5daa3c1c11c380905e2dce630

previous upstream: 0bc12bc4b3dd22cb1bcd34c3ff54225f14abe491
merge-base: 0bc12bc4b3dd22cb1bcd34c3ff54225f14abe491
parent: 8c0631957c850179fc133be802ab16839abd8722

previous upstream: 0bc12bc4b3dd22cb1bcd34c3ff54225f14abe491
merge-base: 0bc12bc4b3dd22cb1bcd34c3ff54225f14abe491
parent: 28bc9ac70d5dab1e4a55c63b3ea6c34629062b51

Adding following to ignore list:
    ^47c94110decc765eab3e606b13da0eedbfabe823

Found the previous import merge:
    7a5a28e59ac76d14a8d2b8432ef70311976bafc1

Walking the changes between found commit and target, excluding
those behind the previous import or merged as an additional
branch during the previous import
    git rev-list --topo-order ['--cherry-pick', '--left-only'] hp/prerelease/mitaka...stable/mitaka ^47c94110decc765eab3e606b13da0eedbfabe823 ^0bc12bc4b3dd22cb1bcd34c3ff54225f14abe491 ^7a5a28e59ac76d14a8d2b8432ef70311976bafc1 --

Walking the changes between found commit and target, excluding
those behind the previous import or merged as an additional
branch during the previous import
    git rev-list --topo-order ['--cherry-pick', '--left-only'] 7a5a28e59ac76d14a8d2b8432ef70311976bafc1...stable/mitaka ^47c94110decc765eab3e606b13da0eedbfabe823 ^0bc12bc4b3dd22cb1bcd34c3ff54225f14abe491 ^7a5a28e59ac76d14a8d2b8432ef70311976bafc1~1 --

commits found:
    b746faa629cb2b178b6f988a171ec4c24509d572
    b66c87d2bf38fab51c9acaaa269b828053824404
    5a18ff213a9824bd91b3313ff08db8366cc96b80
    a086cc5466e759843cc5a4002fb0500ceb5982e0
    f716d76df03d080651a41c5e5bcbd72dec8744d3
    903173e1ac39099eca5cac69b6af8063f993b430
    43b9d0d734ca1736e040f76193b51f6ba69f544b
    c255028efdcf680d18d9bd7d03e9e52a55f0ed22
    9c997bdf1c3099ae5e29b87ba506aaf532e7a2ab
    8c0631957c850179fc133be802ab16839abd8722
    bf60247966cab6e5daa3c1c11c380905e2dce630
    7a5a28e59ac76d14a8d2b8432ef70311976bafc1

...snip...

Import cancelled
Script done, file is git-upstream-import.log