we need tomcat in %post section

this was introduced in commit 10b0a7f4592f86cb1e02bcd15eb88746f27150e0
and later (accidentally) removed during Pulpv2 merge

Putting it back
912442-candlepin-cert - do not overwrite candlepin-upstream-ca.crt
Merge pull request #1613 from thomasmckay/912442-candlepin-cert

912442-candlepin-cert - do not overwrite candlepin-upstream-ca.crt
Merge pull request #1600 from xsuchy/pull-req-tomcat

we need tomcat in %post section