[cri-o-release-1.14] layerStore.Load(): avoid double-locking the mounts list for Save

[nalind]

If we need to re-save the layers list when we've loaded it, to either solve a duplicate name issue or to clean up a partially-constructed layer, don't make the mistake of attempting to take another lock on the mounts list.

Cherry picks #425 for the cri-o-release-1.14 branch.

[rhatdan]

LGTM
@umohnani8 @vrothberg PTAL Not sure why Ubuntu is breaking all the time, this is usually where I whine at @cevich

[umohnani8]

LGTM

[cevich]

sigh it's because Ubuntu is simply broken...let me take a peek...

[cevich]

...sigh, oh this again...yep, it's a broken design.

[+0184s] E: Unable to acquire the dpkg frontend lock (/var/lib/dpkg/lock-frontend), is another process using it?
[+0184s] ##### (failed with exit: 100)
[+0184s] ##### (exceeded 5 attempts)

I believe this is fixed by #408 which is blocked by #419 😞

[cevich]

I think I see a way to workaround this...will open a PR.

[cevich]

#428