classes/updatehub-image-tasks: improve error reporting
classes/updatehub-image-tasks: improve error reporting

When failing we should show the error in output so we avoid using Python
functions for uhuarchive and uhupush as it isn't required.

Signed-off-by: Otavio Salvador <1d31b11c1b92bf5d043d36edfe7174db39a6b891@ossystems.com.br>

UpdateHub/meta-updatehub,UpdateHub/meta-updatehub,UpdateHub/meta-updatehub