liblog: test: enoent requires userdebug or eng to run

(cherry picked from commit 38dad6c9)

Bypass test if we do not have all the prerequisites to run this check
of liblog failure propagation.  We need to be root, or be able to
call su, in order to temporarily stop logd to measure the error
response from liblog.  Basically a "user" build can not have the
levers to deny or fail the logger, preventing our ability to run the
liblog.enoent test.

Test: CTS: User: liblog#enoent
Test: remove ro.debuggable line from /default.prop,
      run liblog-unit-tests --gtest_filter=*.enoent
Bug: 62030441
Change-Id: I52177b8dd3c66d433bddf630e840ee088e13cddc