check_test_cases: Unify walk_compat_sh and walk_opt_sh into one

walk_compat_sh and walk_opt_sh are basically the same now, so:

 * Merge them into one function.
 * Use the --list-test-cases option for both of them.
 * Rename this merged function as collect_from_script which seems
   more appropriate as since it isn't iterating the script but
   calling it.

Signed-off-by: Tomás González <tomasagustin.gonzalezorlando@arm.com>
diff --git a/tests/compat.sh b/tests/compat.sh
index de9dc40..cb15176 100755
--- a/tests/compat.sh
+++ b/tests/compat.sh
@@ -129,7 +129,7 @@
     printf "            \tAlso available: GnuTLS (needs v3.2.15 or higher)\n"
     printf "  -M|--memcheck\tCheck memory leaks and errors.\n"
     printf "  -v|--verbose\tSet verbose output.\n"
-    printf "     --list-test-case\tList all potential test cases (No Execution)\n"
+    printf "     --list-test-cases\tList all potential test cases (No Execution)\n"
     printf "     --outcome-file\tFile where test outcomes are written\n"
     printf "                   \t(default: \$MBEDTLS_TEST_OUTCOME_FILE, none if empty)\n"
     printf "     --preserve-logs\tPreserve logs of successful tests as well\n"
@@ -144,7 +144,7 @@
 }
 
 # list_test_case lists all potential test cases in compat.sh without execution
-list_test_case() {
+list_test_cases() {
     for MODE in $MODES; do
         for TYPE in $TYPES; do
             for VERIFY in $VERIFIES; do
@@ -192,9 +192,9 @@
                 MEMCHECK=1
                 ;;
             # Please check scripts/check_test_cases.py correspondingly
-            # if you have to modify option, --list-test-case
-            --list-test-case)
-                list_test_case
+            # if you have to modify option, --list-test-cases
+            --list-test-cases)
+                list_test_cases
                 exit $?
                 ;;
             --outcome-file)
@@ -1254,7 +1254,7 @@
 }
 
 # uniform_title <CLIENT> <SERVER> <STANDARD_CIPHER_SUITE>
-# $TITLE is considered as test case description for both --list-test-case and
+# $TITLE is considered as test case description for both --list-test-cases and
 # MBEDTLS_TEST_OUTCOME_FILE. This function aims to control the format of
 # each test case description.
 uniform_title() {