lmkd: test: access /sys/module/lowmemorykiller/ as u:r:shell:s0

lmkd_unit_test gets an selinux violation when run unprivileged:

lmkd_unit_test: type=1400 audit(0.0:???): avc: denied { search } for
    name="lowmemorykiller" dev="sysfs" ino=??? scontext=u:r:shell:s0
    tcontext=u:object_r:sysfs_lowmemorykiller:s0 tclass=dir
    permissive=0

resulting in log noise.  Check for INKERNEL_MINFREE_PATH existence
after known to be escalated as root user to suppress noise.

Test: lmkd_unit_test as unprivileged user, there should be no audits.
Change-Id: Ia5c7824e7070c98ee6eea20ca53097e4e56d61b6