Move ENOSPC tests to libfiemap.

These tests are still giving us trouble. Move them to libfiemap, which
(1) is closer to the source of implementation, and (2) allows us to
re-use the temporary filesystem code. This won't perturb the state of
the actual device.

The new test creates a 64MB ext4 or f2fs mount point as a sandbox, which
should be much safer.

Bug: 285197715
Test: fiemap_writer_test
Change-Id: I33502d49613be4f269a80e5c632514fc56a0246a