tests: Fix regex escaping in test-summary-view.sh

There were some regex special characters in the pattern strings, which I
think were causing the test to fail on some Travis builds due to using
an invalid regex.

Fix that by matching using fixed strings instead. We don’t need regexes
here. Use a new assert_file_has_content_literal to do that for us.

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

Closes: #838
Approved by: cgwalters

tests/libtest-core.sh

@@ -85,6 +85,13 @@ assert_file_has_content () {
     fi
 }
 
+assert_file_has_content_literal () {
+    if ! grep -q -F -e "$2" "$1"; then
+        sed -e 's/^/# /' < "$1" >&2
+        fatal "File '$1' doesn't match fixed string list '$2'"
+    fi
+}
+
 assert_symlink_has_content () {
     if ! test -L "$1"; then
         echo 1>&2 "File '$1' is not a symbolic link"