Fix bionic-unit-tests-static crash

The crash happens because for static executables call to dlopen
results in crash. This change moves dlopen() == nullptr check
from static variable to a functions so that the dlopen crash only
affects tests calling dlopen but not the whole executable.

Also make static tests report crashes to debugerd

Test: run bionic-unit-tests-static (for arm 32 and 64)
Bug: http://b/34129417
Change-Id: I7c4d8caf2a43250234fe24496b1c95eab572769f