This patch replaces the legacy retrying library with the newer
and more convenient tenacity one, taking into account that:
1) retrying uses milliseconds for wait times, but tenacity uses seconds;
2) retrying has a lot of numeric arguments for specifying behaviour
of decorated functions, while tenacity has a few of them, which are
specialized objects, thus making the retry-decorator more flexible.
Change-Id: I4b165d37b2ecc210f2b94c103b73eaab51529261
Closes-Bug: #1635404
1a2370ac91