bootscript-uboot: fix test -z cases
During work on new boot logo tasks (YT-129 and YT-130) we found that our U-Boot scripts do not work properly in some environments. After debugging, we found a root cause - a condition under test should be put in double quotes:
u-boot=> pri variable
## Error: "variable" not defined
u-boot=> if test -z $variable; then echo 123; fi
u-boot=> if test -z "$variable"; then echo 123; fi
123
Current MR fixes this issue.
Edited by Mikhail Vanyulin