Add fiemap_writer_test to VTS.

Note: fiemap_writer_test's default argument now defaults to
/data/local/unencrypted or /data (whichever exists), since there is no
way to pass arguments via AndroidTest.xml.

Bug: 129000341
Test: vts-tradefed run commandAndExit vts-kernel --primary-abi-only --module VtsFiemapWriterTest
Change-Id: I8cc2e39e170b26b53cf0a829b308171890ae82fd