When setting perf events, the enabled/disabled perf events are not
listed. Since we know which events were changed it's possible to
print out the values on successful set, such as :

    virsh perf Domain --enable instructions --disable cache_misses
    instructions   : enabled
    cache_misses   : disabled

Created a helper to print the messages - use the vshPrintExtra to
adhere to the --quiet|-q option being set by some script. This will
cause the get code to print nothing, but will return success/failure.
Signed-off-by: NNitesh Konkar <nitkon12@linux.vnet.ibm.com>