wic: add --fixed-size wks option

Added new option --fixed-size to wks. The option can be used to indicate
the exact size of a partition. The option cannot be added together with
--size, in which case an error will be raised. Other options that
influence automatic partition size (--extra-space, --overhead-factor),
if specifiec along with --fixed-size, will raise an error.

If it partition data is larger than the amount of space specified with
--fixed-size option wic will raise an error.

(From OE-Core rev: fdd217ba874bd480e0180830fe2e6bd54dde19d9)

Signed-off-by: Maciej Borzecki <maciej.borzecki@rndity.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/lib/wic/utils/partitionedfs.py

@@ -210,7 +210,7 @@ class Image():
             msger.debug("Assigned %s to %s%d, sectors range %d-%d size %d "
                         "sectors (%d bytes)." \
                             % (part['mountpoint'], part['disk_name'], part['num'],
-                               part['start'], part['start'] + part['size'] - 1,
+                               part['start'], disk['offset'] - 1,
                                part['size'], part['size'] * self.sector_size))
 
         # Once all the partitions have been layed out, we can calculate the