imcv: Fix race condition when initializing loggers

The initialization order of global variables is not defined across
different compilation units. Using functions to access these objects
fixes the problem. However, this is not guaranteed to be thread safe
before C++11.

Without that fix, the program crashed in FileCertManager::FileCertManager
because logger is (smart) NULL.

Signed-off-by: Bernhard Walle <bernhard.walle@ncp-e.com>