esxi: reduce cache invalidation time to 30s

Reduce the time the cache stays valid from 60s to 30s, while this
could double the amount of requests in the worst case, it's still not
that frequent and also halves the maximal time a user has to wait to
see changes on the ESXi side to appear here.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

src/PVE/Storage/ESXiPlugin.pm

@@ -115,7 +115,7 @@ my sub check_esxi_import_package : prototype() {
 my sub is_old : prototype($) {
     my ($file) = @_;
     my $mtime = (CORE::stat($file))[9];
-    return !defined($mtime) || ($mtime + 60) < CORE::time();
+    return !defined($mtime) || ($mtime + 30) < CORE::time();
 }
 
 sub get_manifest : prototype($$$;$) {