tests: rework error handling and stop overusing g_error()

tests: rework error handling and stop overusing g_error()

GLib recommends using g_error() only for programming errors and
unrecoverable situations. It calls abort() and triggers a core dump. This
means that if we encounter an error when running a test case, we'll
exit immediately and leave a "leaked" GPIO simulator in configfs.

Rework the error handling: use g_error() only when a programming bug is
encountered (e.g. invalid enum value) while everywhere else use the
regular GError-based error handling. This way, in case of an error in
libgpiosim, we'll simply fail the current test case and release all
resources as usual.

In order not to pollute the test cases with error handling, let's hide the
actual error checking behind macros for g_gpiosim_chip_new() and
g_gpiosim_chip_get_value(). For g_gpiosim_chip_set_pull() let's just emit
a log and do nothing as the test case in question will inevitably fail if
the expected value is not correctly read back.

In order for the chip to get a failing constructor, we need to link the
test-suite against the entire libgio, not only libgobject (for the
GInitable interface).

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>