Add error info when s4 is not available

s4 check could be failed because the rest of guest disk space is less than guest memory.
Will print the rest of disk space and guest memory and guest free memory in the error info.

BZID:1170490

Change from v1:
    Change the error info
    Compare FreeDisk and Mem * 75% instead of Mem

Signed-off-by: Chengyou Liu <cheliu@redhat.com>