Adapt modules and unit tests to use C symbols instead of internal kernel C++ API

[wkozaczuk]

The commit af2d371 introduced the ability to build OSv kernel with most symbols but a subset of glibc hidden.
The regular Linux glibc apps should run fine on such kernel, but unfortunately many unit tests and various internal OSv apps (so-called modules) do not as they had been coded to use many internal C++ API symbols. In order to make those programs run on a kernel built with most symbols and standard C++ library hidden, we need to change them to either use suitable standard glibc symbols or expose some of the C++ API as C functions just like it was done for the httpserver-monitoring-api module (see 182499c and 891bfcd).
The relevant effort would be quite substantial and I doubt we will ever finish adapting all apps. So I am listing individual programs below in the order of importance:

• libtools (both lsroute.cc and ifconfig.cc use BSD internal API); ideally we should try to change some standard Linux facility or possibly expose a pseudo-file under /proc
• non-read-only part of httpserver-api
• cloud-init
• golang (wrapper to bootstrap go programs built as a shared library), uses only 2 C++ symbols
• unit tests
  • 31 out of 140 tests reference some internal C++ API; the discussion on the emailing list describes the details

I am on purpose not mentioning run-java and any java programs as I do think we have any appetite to touch this - please read this to understand why.