[RAUC] improve sysdata handle, post and pre install

The script for sysdata handler has been modified to make sure it works on x86 architecture. These changes are need due to the different definition of bootargs, saved and read from the /proc/cmdline. In the common case the cmdline is defined with root=/dev/<boot_device> and bootdevice=<boot_device> so the scripts extract from this command all the information needed. In other cases the bootdevice is not defined and the only variable available is the root. In this case are considered two possibilities:

• the first one consider the root=PARTUUID=, so to extract the information needed it is necessary to use another function that iterates all partitions to find the right PARTIONUUID;
• the second one consider the root=/dev/<boot_device> but without the bootdevice variable so in the scripts has been build a command line in which the information could be extracted cutting the right thing from the /proc/cmdline

Signed-off-by: carlo carlo.ferriolo@seco.com