Fix e2fsck's get_size logic so it will work with the Linux floppy driver

Fix e2fsck's get_size logic so it will work with the Linux floppy driver

The Linux floppy driver is a bit different from the other block device
drivers, in that if the device has been opened with O_EXCL, it disallows
another open(), even if the second open() does not have the O_EXCL flag.
So this patch moves the call to ext2fs_get_device_size() so that if it
returns EBUSY, e2fsck can close the filesystem, retry the device size,
and then reopen it.  This rather complicated approach is required since
we need to know the blocksize of the filesystem before we can call
ext2fs_get_device_size().

Addresses Debian Bug: #410569

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>