testsuite: put flux bin before ompi bin

[garlick]

Problem: the test suite pushed the ompi bin directory in front of the flux bin directory, but when ompi is installed as a system package, this places /usr/bin in front of a possibly side installed flux-core path.

This was noted to be the case on LLNL's lassen system.

Place the flux path in front of the ompi path when setting up sharness test paths.

This was first noted in #85.

[codecov[bot]]

Codecov Report

Merging #86 (8ec8e1b) into main (5201666) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #86   +/-   ##
=======================================
  Coverage   79.01%   79.01%           
=======================================
  Files          12       12           
  Lines        1382     1382           
=======================================
  Hits         1092     1092           
  Misses        290      290           

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