IMPALA-1572: Use DecimalFormat instead of String.format() in PrintUtils.

String.format() appears to have some kind of race / set-up problem
on JDK7 but not JDK6. This patch works around the problem by using
a different class for string formatting.

Change-Id: I759f8cf012bfa9d820b50dac2417d2f8d7478700
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/5493
Tested-by: jenkins
Reviewed-by: Alex Behm <alex.behm@cloudera.com>