Until now, for dualboot systems, all boot variables were calculated on each boot depending on the value of the
'active_system'. These variables are used to boot the device but were not saved, which could lead to a missmatch
between their value in the environment and their required values to correctly boot the system. This commit
simplifies a bit the variables calculation and adds a block to synchronize their value in the environment.
Signed-off-by: David Escalona <david.escalona@digi.com>