TEST-46-HOMED fails on ext4 because the filesystem is deemed to small
for activation by cryptsetup. Let's bump the minimal filesystem size for
ext4 a bit to be in the same ballpark as ext4 and btrfs to avoid weird
errors due to impossibly small filesystems.
Also use U64_MB while we're touching this.
Having these named differently than the test itself mostly creates
unecessary confusion and makes writing logic against the tests harder
so let's rename the testsuite-xx units and scripts to just use the
test name itself.