ENOSPC if flashing kernel after PNOR

[ghost]

At least on some machines (notably Briggs&Stratton), the /tmp filesystem on the BMC doesn't have much space, so when we rsync over P8DTU.pnor before flashing it, we use up a fair amount of /tmp space. So much, that if I invoke op-test again to flash a new BOOTKERNEL, there's not enough room in /tmp to transfer the bootkernel over.

With ENOSPC transferring images, we don't really pick up that error elegantly and you have to resort to the op-test debug log to find out what went wrong.

We should possibly remove images (such as pnor and individual LIDs) from /tmp on the bmc after we've flashed them to help avoid these kinds of problems.