build: Add ‘devel’ or ‘release’ to OSTREE_FEATURES for test-symbols.sh

test-symbols.sh was looking for the DevelBuild string, which is actually
part of the output from `ostree --version`, not $OSTREE_FEATURES.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Closes: #948
Approved by: cgwalters

tests/test-symbols.sh

@@ -22,7 +22,7 @@ set -xeuo pipefail
 echo '1..3'
 
 released_syms=${G_TEST_SRCDIR}/src/libostree/libostree-released.sym
-if echo "$OSTREE_FEATURES" | grep --quiet --no-messages "DevelBuild"; then
+if echo "$OSTREE_FEATURES" | grep --quiet --no-messages "devel"; then
     devel_syms=${G_TEST_SRCDIR}/src/libostree/libostree-devel.sym
 else
     devel_syms=