Tweak the regular expression used for extracting system test results

Tweak the regular expression used for extracting system test results

The current regular expression used for extracting system test results
from systests.output, "^R:", is anchored at the start of a line, which
prevents colored system test output from being properly processed.  As
just "R:" would arguably be too general, extend the pattern a bit to
ensure it will only match lines containing system test results.

(cherry picked from commit 9006d6dbbdad0bd2969c401e1e6bb468ffc85324)