test.lua: Add basic test library and helpers

tests/lua/test_helper.lua

+function setup_path()
+  local str = require("debug").getinfo(2, "S").source:sub(2)
+  local cwd = str:match("(.*/)")
+  local bpf_path = cwd.."/../../src/lua/?.lua;"
+  local test_path = cwd.."/?.lua;"
+  package.path = bpf_path..test_path..package.path
+end
+
+setup_path()
+
+USE_EXPECTED_ACTUAL_IN_ASSERT_EQUALS = false
+EXPORT_ASSERT_TO_GLOBALS = true
+require("luaunit")
+
+BCC = require("bcc.init")
+BPF = BCC.BPF
+log.enabled = false