integration fix: change the way to print the version
Using "system" to call "git log" is too error-prone. In the test setup, lte-softmodem was blocked because "git log" uses a pager ("less") and the pager was waiting for the user to press enter. We could pass "--no-pager" to "git log" but then what if someone runs the softmodem out of the source tree? cmake defines PACKAGE_VERSION, we can use that instead, as is done in openair-cn.