ostree-repo: Make the lock with a long-lasting FD

glnx_make_lock_file requires that the dfd passed in survives the
lifetime of the lock. Since dfd_iter.fd gets cleaned up after the
function returns, this isn't the case. dfd_iter.fd should be equivalent
to tmpdir_dfd, since we iter on ".", and that survives past the
function, so just use that instead.

Closes: #591
Approved by: cgwalters

tests/test-admin-deploy-bootid-gc.sh

@@ -51,7 +51,7 @@ fi
 newstagepath=$(ls -d sysroot/ostree/repo/tmp/staging-${NEW_TEST_BOOTID}-*)
 assert_has_dir "${newstagepath}"
 env OSTREE_BOOTID=${NEW_TEST_BOOTID} ${CMD_PREFIX} ostree admin deploy --karg=root=LABEL=MOO --karg=quiet --os=testos testos:testos/buildmaster/x86_64-runtime
-newstagepath=$(ls -d sysroot/ostree/repo/tmp/staging-${NEW_TEST_BOOTID}-*)
+newstagepath=$(echo sysroot/ostree/repo/tmp/staging-${NEW_TEST_BOOTID}-*)
 assert_not_has_dir "${stagepath}"
 assert_not_has_dir "${newstagepath}"