Add test for big disks on multipath

[jmarrero]

The test needs to do something like:

cosa run -c --qemu-size=1T --qemu-memory=6096 --qemu-multipath=true --kargs='rd.multipath=default root=/dev/disk/by-label/dm-mpath-root rw'

and verify that we boot and the agcount is low by running:

xfs_info /

the output should look similar too:
meta-data=/dev/mapper/mpatha4 isize=512 agcount=4, agsize=201293759 blks

notice the agcount is 4.