rump_fs: Transition to new API

The rump libraries and the rump_fs component are now conform to the new base
API. Also the I/O back end should be running stable now.

issue #2224

repos/dde_rump/run/rump_ext2.run

@@ -85,7 +85,7 @@ install_config $config
 set boot_modules {
 	core ld.lib.so init timer test-libc_vfs ram_blk
 	rump.lib.so rump_fs.lib.so rump_fs
-	ext2.raw libc.lib.so
+	ext2.raw libc.lib.so libm.lib.so
 }
 
 build_boot_image $boot_modules