Disable call to setpriority() in pbxt. This caused mysqld to run with nice priority -19, which was far from optimal.

mysql-test/suite/innodb/r/innodb_bug60049.result:
  Updated results
mysql-test/suite/innodb/t/innodb_bug60049.test:
  Force global.innodb_fast_shutdown to 0 as test require it
mysql-test/suite/innodb_plugin/t/innodb_bug60049.test:
  Force global.innodb_fast_shutdown to 0 as test require it
storage/pbxt/src/pthread_xt.cc:
  Disable call to setpriority()