west_commands: sign: suppress imgtool prints
If `args.quiet` is set, suppress the useless `print` statements output
by `imgtool` (mcuboot script) by capturing `stdout`.
Old output:
```
[44/44] Linking C executable zephyr/zephyr.elf
Memory region Used Size Region Size %age Used
FLASH: 415192 B 824 KB 49.21%
RAM: 163124 B 256 KB 62.23%
IDT_LIST: 0 GB 2 KB 0.00%
image.py: sign the payload
image.py: sign the payload
```
New output:
```
[44/44] Linking C executable zephyr/zephyr.elf
Memory region Used Size Region Size %age Used
FLASH: 415192 B 824 KB 49.21%
RAM: 163124 B 256 KB 62.23%
IDT_LIST: 0 GB 2 KB 0.00%
```
Signed-off-by: Jordan Yates <jordan.yates@data61.csiro.au>
1 file changed
