binman: Simplify the entry test

binman: Simplify the entry test

The current test for the 'entry' module is a bit convoluted since it has
to import the module multiple times. It also relies on ordering, in that
test1EntryNoImportLib() must run before test2EntryImportLib() if they are
running in the same Python process.

This is unreliable since neither the ordering of tests nor the process
that they run in is defined.

Fix this by always reloading the entry in these two tests. Also add a
check that the expected value of have_importlib is obtained.

This corrects a code-coverage problem in the 'entry' module on some
systems.

Signed-off-by: Simon Glass <sjg@chromium.org>