Fix for issue #297

[mihaibudiu]

that this fix allows action_profile objects to be declared outside tables. As a side-effect, this change will enable the sharing of an action_profile between multiple tables.

Note that this fix does not allow action_selectors to be declared outside tables, just action_profiles.

[antoninbas]

The produced JSON for the test program you are checking-in is rejected by bmv2:

simple_switch: P4Objects.cpp:1063: int bm::P4Objects::init_objects(std::istream*, bm::LookupStructureFactory*, int, size_t, std::shared_ptr<bm::TransportIface>, const std::set<std::pair<std::__cxx11::basic_string<char>, std::__cxx11::basic_string<char> > >&, const bm::P4Objects::ForceArith&): Assertion `table_type == "indirect" || table_type == "indirect_ws"' failed.
Aborted (core dumped)

The issue seems to be that your "indirect" table is missing the "type" attribute. However, your "indirect_ws" table does not suffer from this issue.

[mihaibudiu]

Hopefully this change fixes the problem @antoninbas pointed out.
I have added an empty stf file, which will cause the test to attempt to load the json into simple_switch.