shared.cfg: Small fix, add a missing parameter

Signed-off-by: Shuping Cui <scui@redhat.com>
Merge pull request #1863 from spcui/usb_fix

shared.cfg: Small fix, add a missing parameter
virttest.utils_misc: add SELinux boolean manager

Signed-off-by: Alex Jia <ajia@redhat.com>