Update test configuration to pass code style checks

Update `checkpatch.pl` configuration and the `_test/run_test.sh` shell
script to pass code style checks.

Signed-off-by: Razvan Deaconescu <razvan.deaconescu@upb.ro>

.checkpatch.conf

@@ -32,3 +32,6 @@
 
 # Ignore SPLIT_STRING, quoted strings can be split on multiple lines.
 --ignore SPLIT_STRING
+
+# Ignore STRCPY, as `strscpy()` is only present in the Linux source.
+--ignore STRCPY

tests/_test/run_test.sh

@@ -23,7 +23,7 @@ DEBUG_=0
 
 DEBUG()
 {
-    if test "x$DEBUG_" = "x1"; then
+    if test "$DEBUG_" = "1"; then
         "$@" 1>&2
     fi
 }
@@ -80,7 +80,7 @@ test_do_fail()
 {
     points=$1
     printf "failed  [ 0/%02d]\n" $max_points
-    if test "x$EXIT_IF_FAIL" = "x1"; then
+    if test "$EXIT_IF_FAIL" = "1"; then
         exit 1
     fi
 }