unit test setup

[fntlnz]

What type of PR is this?

/kind feature

What this PR does / why we need it:

This PR adds support to use catch2 as a testing framework, initially it allows only to test falco_engine but it will be expanded to other areas as soon as we extract functionalities into libraries.

There's no actual tests in this PR since this one is to setup the environment that will then be used in other PRs checking in the tests.

Here's how a unit test will look like:

#include <catch.hpp>

using namespace std;
using Catch::Matchers::Equals;

TEST_CASE("someFunction check if false is false") {
    REQUIRE_FALSE(false);
}

Tests will be organized under the tests folder.

For example, falco_engine tests will go under tests/engine using the same structure as for userspace.

For every other type of assertion and details, refer to the the catch2 documentation.

Which issue(s) this PR fixes:

Fixes #686

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

new: unit test setup

[leodido]

/hold
I propose to hold it until we integrate them in Travis.

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: leodido

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• OWNERS [leodido]

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[poiana]

LGTM label has been added.

Git tree hash: 01cc25da86d7eecea8dd41ecfef828caa2171488