[FIX] Use library_dirs for cython linking, link cudatoolkit libs, allow setting UCX install location

[trxcllnt]

This PR is a continuation of #1694. Similar to NVIDIA/cuml#4015, this PR updates setup.py to:

• Use library_dirs instead of runtime_library_dirs when linking Cython.
• Allow overriding UCX lib and include dirs via a UCX_HOME envvar.
• Link cudart, cusparse, and cusolver.

These are necessary to compile the Cython via pip when not inside a conda environment and when UCX is installed to a location other than /usr or /usr/local.

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (branch-21.08@e2ac467). Click here to learn what that means.
The diff coverage is n/a.

@@               Coverage Diff               @@
##             branch-21.08    #1698   +/-   ##
===============================================
  Coverage                ?   59.34%           
===============================================
  Files                   ?       80           
  Lines                   ?     3559           
  Branches                ?        0           
===============================================
  Hits                    ?     2112           
  Misses                  ?     1447           
  Partials                ?        0           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update e2ac467...39fe4be. Read the comment docs.

[BradReesWork]

@gpucibot merge