Fixes filter related fuctions.

When configuration is incorect (unknown or wrong host/service parameter),
exceptions may be risen by business rules parsing in filter related
functions (passed host/service may be None) before error massage may be
displayed.

This fixes this issue by checking that all required parameters are set.
Merge pull request #1039 from geektophe/fix_util_filter

FIX: Fixes filter related fuctions (in business rules processing)