libbladeRF: Moved tests out of libbladeRF/ directory

Because the libbladeRF tests were nested under the libbladeRF build,
they were being built with the include paths, library paths, etc.
used for libbladeRF.

This was masking build issues that libbladeRF users might experience,
such as MS Visual Studio 12 and earlier failing due to a lack of a
stdbool.h header.

Therefore, these tests have been moved in the build hierarchy to avoid
cross-pollination of the libbladeRF build environment. This should
better represent users building against libbladeRF, and make build
issues more apparent.

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! IMPORTANT NOTE !
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   This commit breaks builds on Visual Studio 2012 and earlier.
   This will be addressed in upcoming commits.