resampler-test: Add zero padding.

For the resampler test we create 10 samples and run them through a
resampler and then we try to run run the resampler backwards. This
crashes if our original 10 samples are not enough to produce any output
on the original run.

This patch adds additional zero padding to our original 10 samples. This
way all resample methods produce enough output to run the resampler
backwards.
resampler-test: Change the default rates

The default test case in resampler-test is to run the auto resample
method with some test samples from a rate of 44100Hz to a rate of
44100Hz.

When the rates are equal our resamlper automatically chooses to use the
'copy' resamlpe method (that is no resampling is done). This is quite
useless as our default test case (which is run by make check), so change
the rates to something more sensible.
resampler-test: Refactor out the test code into functions

We have 2 main test cases:
    - run the resampler using only a single sample format
    - run the resampler using all sample formats

This patch simply moves our test cases into separate functions. To
improve readability and reusability.
resampler-test: Change the default test case to test all methods

This changes the default behaviour of our resampler-test if we
don't provide a resmaple method or sample format on the command line.

If neither a method or a sample format is specified we test all
resampling methods.

This way if we run 'make check' all our resampling methods will be
tested.