Ignore some non-interesting filesystem types

Generally, how much space we have in squashfs, or tmpfs shouldn't
interest us. This becomes more relevant in distros like Ubuntu, where
snaps are a thing, and each snap mounts their own FS in a squashfs that
is always full, thus falsifying the output of sysinfo.

plugins/sysinfo/shared/df.c

@@ -26,7 +26,7 @@ int xs_parse_df(gint64 *out_total, gint64 *out_free)
 	FILE *pipe;
 	char buffer[bsize];
 	
-	pipe = popen("df -k -l -P", "r");
+	pipe = popen("df -k -l -P --exclude-type=squashfs --exclude-type=devtmpfs --exclude-type=tmpfs", "r");
 	if(pipe==NULL)
 		return 1;