Add a macro "runselftest" to the spec file for RPM builds.

If its value is 1 (the default), the test suite will be run during
the RPM build.
To prevent that, add this to the rpmbuild command line:
    --define "runselftest 0"
Failures of the test suite will NOT make the RPM build fail!


support-files/mysql.spec.sh:
  Add the "runselftest" macro following the model provided by RedHat.
  
  This code is similar to what we plan to use for ULN RPMs.