Switch module required on Ubuntu 14.04

Fixes the following error on Ubuntu 14.04:

```
Can't locate Switch.pm in @INC (you may need to install the Switch module) (@INC contains: /etc/perl /usr/local/lib/perl/5.18.2 /usr/local/share/perl/5.18.2 /usr/lib/perl5 /usr/share/perl5 /usr/lib/perl/5.18 /usr/share/perl/5.18 /usr/local/lib/site_perl .) at ./mon-put-instance-data.pl line 73.
BEGIN failed--compilation aborted at ./mon-put-instance-data.pl line 73.
```