Initial import of libustctl and libustcomm

Import and clean the libustctl and libustcomm code from the UST git
tree. This import is done at the ust git head commit:
161239e0409832d65cb773a08d364b29945b18a7

Small modifications was needed but nothing major in the API and basic
functionnalities.

Signed-off-by: David Goulet <david.goulet@polymtl.ca>