Refactor ebpf test runner

[fearful-symmetry]

How to run tests

This completely refactors the go testrunner for EventsTrace. This has a number of advantages:

• tests can now be run locally, without bluebox
• You can run individual tests
• Tests are structured in the "standard" golang way, and take advantage of the go stdlib test functionality
• I added a make testbins target for the c test binaries

This also fixes a few known bugs, and probably many more:

• The test runner would sometimes eat stderr messages that occur during startup
• If the test runner got overwhelmed with data from stdout/stderr, it would drop the log data
• If a test failed, it would sometimes hang and time out instead of immediately failing

In addition, I fixed a few bugs in the tests that I ran into while refactoring:

• The tty output would try to use the escape character \x, which is not a valid JSON escape character and broke all the JSON parsers I tried.
• the overlayfs test would try to remove a directory without unmounting it, which would fail

How to run tests

make testbins #make the test binaries in testing/test_bins
cd testing/testrunner
go test -c #compile the test in advance, so we don't need root to have a go environment
# run all tests
sudo ./testrunner.test
# run a single test
sudo ./testrunner.test -test.run TestEbpf/Tcpv6ConnectionClose -test.v

Known issues with individual tests:

• fork_exec.c works by setting the capabilities mask to an identifiable but meaningless mask value; for whatever reason this works in the test environment, but on my machine the new capability set completely breaks the binary.
• create_rename_delete_file_container.c breaks on newer kernels if you try to remove the directories before doing an unmount on ovl_mountpoint, but on the mainline tests, and only the mainline tests (which are actually kind of old), this unmount operation fails with an Invalid Argument error.