Block file size adjustment for ubuntu_xfstests_*

[Po-Hsu Lin]

After switching to use loop devices instead of a scratch drive for the test, we are now using 20G block file for the test.

However we are creating partitions over this size:
sudo parted $DEVICE mklabel -s gpt
sudo parted $DEVICE mkpart -s p1 $FS 1MiB 20000MiB
sudo parted $DEVICE mkpart -s p2 $FS 20001MiB 40000MiB
sudo parted $DEVICE mkpart -s p3 $FS 40001MiB 60000MiB
sudo parted $DEVICE mkpart -s p4 $FS 60001MiB 80000MiB
sudo parted $DEVICE mkpart -s p5 $FS 80001MiB 80500MiB
sudo parted $DEVICE mkpart -s p6 $FS 80501MiB 81000MiB

To do:
* We will need to at least adjust the block file size, preferably knowing why we need up to 81000MiB for the test.