Test rollback-altboot (broken init) fails

[floion]

Tested on imx6ul-var-dart from 2.31.5+rev1 to 2.44.0+rev4

[acostach]

do you recall if this is the case of failed write of bootcount @floion, or something similar? sounds like it and we can probably fix it quickly if that's the case

[acostach]

This PR #117 addresses the issues I found regarding HUP altboot - broken init from 2.31.5 to 2.44.0.

Not sure if what's fixed covers the original root cause. What I encountered was:

1. uboot env size not specified for the case where environment cannot be loaded from emmc. If env loading failed, default one was attempted to be used but it didn't fit the default size (lower than 12k - 0x3000 specified for emmc).

2. fatwrite failure when more than 19 files were present on the boot partition, masked by 1). uboot got stuck trying to write bootcount.

[acostach]

[imx7] altboot from 2.38.3 to 2.71.3, in this particular case however we switch to loading the dtb from the rootfs. the new rootfs has them, the old one does not, so this is expected and should not fail anymore now, starting with 2.71.3.