Fixed cta/CTA#862 Unable to delete tabtest tape pool because it's in an archive route

Here is an example:
```
[itctabuild02] ~ (krb5=ctaadmin1)> cta-admin tapepool add --name steve --vo vo_1 --partialtapesnumber 1 --encrypted false --comment "Steve's tape pool"
[itctabuild02] ~ (krb5=ctaadmin1)> cta-admin archiveroute add --storageclass single_1 --copynb 1 --tapepool steve --comment "Steve's archive route"
[itctabuild02] ~ (krb5=ctaadmin1)> cta-admin tapepool rm --name steve
Cannot delete tape-pool steve because it is used in an archive route
[itctabuild02] ~ (krb5=ctaadmin1)>
```