Support negative dependencies in test cases

The entropy test suite uses a negative dependency "depends_on:!CONFIG_FLAG" for one of its tests. This kind of
dependency (running a test only if some configuration flag is not defined) is currently not supported and instead
results in the respective test case being dropped.

This commit adds support for negative dependencies in test cases.
diff --git a/tests/scripts/generate_code.pl b/tests/scripts/generate_code.pl
index e13a2d0..5d7d219 100755
--- a/tests/scripts/generate_code.pl
+++ b/tests/scripts/generate_code.pl
@@ -194,7 +194,7 @@
 # and make check code
 my $dep_check_code;
 
-my @res = $test_data =~ /^depends_on:([\w:]+)/msg;
+my @res = $test_data =~ /^depends_on:([!:\w]+)/msg;
 my %case_deps;
 foreach my $deps (@res)
 {
@@ -205,7 +205,23 @@
 }
 while( my ($key, $value) = each(%case_deps) )
 {
-    $dep_check_code .= << "END";
+    if( substr($key, 0, 1) eq "!" )
+    {
+        my $key = substr($key, 1);
+        $dep_check_code .= << "END";
+    if( strcmp( str, "!$key" ) == 0 )
+    {
+#if !defined($key)
+        return( 0 );
+#else
+        return( 1 );
+#endif
+    }
+END
+    }
+    else
+    {
+        $dep_check_code .= << "END";
     if( strcmp( str, "$key" ) == 0 )
     {
 #if defined($key)
@@ -215,6 +231,7 @@
 #endif
     }
 END
+    }
 }
 
 # Make mapping code