DM-15851: Clean target files if we are not performing an install

[brianv0]

If we are supplying the --last-failed-no-failures flag (lfnfOpt) with the value of all, then make sure to delete the previous target files before executing the SCons command.

If we are invoking SCons for an install, we set the lfnfOpt = "none", otherwise it's all.

[timj]

I think the commit messsage (or possibly the code itself) should say that the reason we can't always delete the target files is that if the tests skip for the install we still need the JUnit XML file to be around for Jenkins to collect it. Otherwise, install runs, no tests run, Jenkins thinks no tests ran at all.

[timj]

With this ticket branch I'm now getting junk in my shell when I run scons:

pytest: automated test discovery mode enabled.
@rm -f ${{TARGET}} ${{TARGET}}.failed;
        @printf "%s\n" 'running global pytest... ';
        @({2} TRAVIS=1 {0} {1});         export rc="$?";         if [ "$$rc" -eq 0 ]; then             echo "Global pytest run completed successfully";             cp ${{TARGET}} ${{TARGET}}.all || true;             cp ${{TARGET}}.out ${{TARGET}}.out.all || true;         elif [ "$$rc" -eq 5 ]; then             echo "Global pytest run completed successfully - no tests ran";             mv ${{TARGET}}.all ${{TARGET}} || true;             mv ${{TARGET}}.out.all ${{TARGET}}.out || true;         else             echo "Global pytest run: failed with $$rc";             mv ${{TARGET}}.out ${{TARGET}}.failed;         fi;
        
scons: done reading SConscript files.

[timj]

Please fix the spurious output messages and note why this is conditionally needed.