Initialize all stack variables to zero, fix uninitialized loglevel variables

If we want the padding behavior to be always the same (for future
extensibility), we need to set those variables to zero when they are
declared on the stack.

Also fix uninitialized loglevel variables in tests, which were failing
on x86_32 due to this.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>