pmiostat: add -P N flag for N digits of precision (similar to pmrep)
pmiostat: add -P N flag for N digits of precision (similar to pmrep)

This adds the -P N flag for N digits of precision (default 2).
The actual new formatting code and man page update will be in
a follow-up commit.

wuliming/pcp,wuliming/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,wuliming/pcp,wuliming/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,wuliming/pcp,wuliming/pcp,wuliming/pcp,wuliming/pcp,adfernandes/pcp