[tests] Fix setconfig() and make more robust

test/common.bash

@@ -68,9 +68,9 @@ teardown() {
 }
 
 setconfig() {
-    if grep -q "$2 =" "${BATS_TMPDIR}/$1"; then
-        sed -i "s/^$2.*/$2 = $3/" "${BATS_TMPDIR}/$1"
+    if grep -qe "$2\s\+=" "${BATS_TMPDIR}/$1"; then
+        sed -i "s/^$2\s\+=.*/$2 = $3/" "${BATS_TMPDIR}/$1"
     else
-        echo "$2 = $3/" >> "${BATS_TMPDIR}/$1"
+        echo "$2 = $3" >> "${BATS_TMPDIR}/$1"
     fi
 }