ext4_utils: add filesystem capabilities support.

ext4_utils: add filesystem capabilities support.

Add support for specifying filesystem capabilities when
creating a new filesystem.

The combination of SELinux extended attributes plus
filesystem capability extended attributes is too big
to fit inside one inode entry. Because of this, I added
support to ext4_utils to create an xattr block and link
the inode to that block. We continue to try to fit
everything inside the inode if possible, but fall over to
creating a block if the extended attribute is too big.

Change-Id: I40ebb63975b15ecd8c565486e171b4d50cd4dfaa