realtime profile should not add 'isolcpus=' when realtime-variables.conf has empty isolated_cores

[olysonek]

When realtime-variables.conf has isolated_cores="", tuned adds 'isolcpus=' to the kernel boot parameters. Tuned should accept an empty string for isolated_cores and put nothing about isolcpus on the kernel cmd line.

Steps to Reproduce: 1.in realtime-variables.conf, put isolated_cores="" 2. tuned-adm profile realtime 3. reboot

This results in "isolcpus=" being placed on the kernel command line, but it should not be placed there.

Original bug report: https://bugzilla.redhat.com/show_bug.cgi?id=1755854