Don't Execute() on non-Operational hosts, WARN on them though.
Rename filter option to filters.
remove _and_warn from method name
Merge cleanup
Merge pull request #44 from Nextdoor/fix_execute_on_booting_instances

Don't Execute() on non-Operational hosts, WARN on them though.
Fix optional parameter errors.
Merge pull request #45 from Nextdoor/fix_tests

Fix optional parameter errors.