CI/travis/lib.sh: add script that handles LDIST & other common stuff
CI/travis/lib.sh: add script that handles LDIST & other common stuff

This will handle getting the `get_ldist` script from libiio, since that
logic is common and should be re-used.

It also sets the LIBIIO_BRANCH env var to be used during this build.

Signed-off-by: Alexandru Ardelean <685557f6b7c225d86b536740313ed51b24843a58@analog.com>

analogdevicesinc/libad9361-iio,analogdevicesinc/libad9361-iio,analogdevicesinc/libad9361-iio,analogdevicesinc/libad9361-iio