rtas-get-time-of-day, rtas-get-time-of-day-base, rtas-set-time-of-day in ubuntu_kvm_unit_tests failed on Power8 with Eoan

[Po-Hsu Lin]

Issue found on node P8 node modoc (passed with power9 baltar) with Eoan

All these 3 tests failed with:
    qemu-system-ppc64: Requested safe cache capability level not supported by kvm, try cap-cfpc=broken

Log:
 Running 'ppc64_cpu --smt=off'
 Running '/home/ubuntu/autotest/client/tmp/ubuntu_kvm_unit_tests/src/kvm-unit-tests/tests/rtas-get-time-of-day'
 [stdout] BUILD_HEAD=e2c275c4
 [stdout] timeout -k 1s --foreground 5 /usr/bin/qemu-system-ppc64 -nodefaults -machine pseries,accel=kvm -bios /tmp/tmp.Thimcho6Av -display none -serial stdio -kernel /tmp/tmp.P0LCYS8Wqf -smp 1 -append get-time-of-day date=1580953361 # -initrd /tmp/tmp.FME1mdmqJi
 [stderr] qemu-system-ppc64: Requested safe cache capability level not supported by kvm, try cap-cfpc=broken
 [stdout] FAIL rtas-get-time-of-day
 Running 'ppc64_cpu --smt=on'

 Running 'ppc64_cpu --smt=off'
 Running '/home/ubuntu/autotest/client/tmp/ubuntu_kvm_unit_tests/src/kvm-unit-tests/tests/rtas-get-time-of-day-base'
 [stdout] BUILD_HEAD=e2c275c4
 [stdout] timeout -k 1s --foreground 5 /usr/bin/qemu-system-ppc64 -nodefaults -machine pseries,accel=kvm -bios /tmp/tmp.ySV1lsLBZb -display none -serial stdio -kernel /tmp/tmp.9IKscBYm0v -smp 1 -rtc base=2006-06-17 -append get-time-of-day date=1150502400 # -initrd /tmp/tmp.S5yW7PrRTl
 [stderr] qemu-system-ppc64: Requested safe cache capability level not supported by kvm, try cap-cfpc=broken
 [stdout] FAIL rtas-get-time-of-day-base
 Running 'ppc64_cpu --smt=on'

 Running 'ppc64_cpu --smt=off'
 Running '/home/ubuntu/autotest/client/tmp/ubuntu_kvm_unit_tests/src/kvm-unit-tests/tests/rtas-set-time-of-day'
 [stdout] BUILD_HEAD=e2c275c4
 [stdout] timeout -k 1s --foreground 5 /usr/bin/qemu-system-ppc64 -nodefaults -machine pseries,accel=kvm -bios /tmp/tmp.9ie1RxJPCz -display none -serial stdio -kernel /tmp/tmp.UkNdFK9eYI -smp 1 -append set-time-of-day # -initrd /tmp/tmp.1KJAW1ljtX
 [stderr] qemu-system-ppc64: Requested safe cache capability level not supported by kvm, try cap-cfpc=broken
 [stdout] FAIL rtas-set-time-of-day
 Running 'ppc64_cpu --smt=on'