pmseries: support scalar constant multiplication

[andreasgerstmayr]

The kernel.cpu.util.sys derived metric is defined as:

kernel.cpu.util.sys = (100 * rate(kernel.all.cpu.sys)) / hinv.ncpu

It would be great if the same expression is also supported with pmseries:

$ pmseries "(100 * rate(kernel.all.cpu.sys)) / hinv.ncpu"
pmseries: [Error] cannot parse given string

(100 * rate(kernel.all.cpu.sys)) / hinv.ncpu
^ -- syntax error


$ pmseries "100 * rate(kernel.all.cpu.sys) / hinv.ncpu"
pmseries: [Error] cannot parse given string

100 * rate(kernel.all.cpu.sys) / hinv.ncpu
^ -- syntax error