shared.cfg: Small fix for s3_support_chk_cmd

For latest windows guest, s3 support log in multi lines, like:
    The following sleep states are available on this system:
        Standby (S3)

old s3_support_chk_cmd cannot find str for multi lines,
so update it.

Signed-off-by: Shuping Cui <scui@redhat.com>
Merge pull request #1912 from spcui/guest_s3_fix

shared.cfg: Small fix for s3_support_chk_cmd