Improve PLRsearch yet again

Improve PLRsearch yet again

Logic improvements for rls1908 and post-pylint fixes:

+ Reduce search time to 30 minutes.
+ Use average instead alternating loads.
+ Rework log/exp avg/stdev from two estimates.
+ Introduce and use pessimistic variance of dual trackers.
+ Introduce safe_exp to use when None does not skip code.
+ Use dot relative imports (instead of disabling pylint).
+ Complete docstrings for simpler functions.
+ Append docstrings to named tuples.
+ Somewhat unify docstrings related to the same arguments.
+ Slightly improve intentation.
+ State named tuples as rtype where used.
+ Add returns and rtype to __repr__ where missing.
+ Return what docstring say (or update them).
+ Explicit copying for vector and matrix values.

Change-Id: I884c68b4839c5df5e8bef95e463666599603a0ff
Signed-off-by: Vratko Polak <vrpolak@cisco.com>
(cherry picked from commit fbbc47359e3f7b59bbd5a84d85c673374933a50a)