liblog#__android_log_btwrite__android_logger_list_read fail

With replaced AOSP system.img, adb can be root by other test.
The fail is caused by the reason that logdw is still active after
__android_log_close().

This test has a potential bug.
proc/net/unix may contain '\0', then "grep" command will treat this file
as a bianry file.
Using "grep -a" instead of "grep" could be a safer way to get the right
results from bianry file.

bug: 112250722
Test: Build CTS
Test: Pixel 2 XL PPP5.180610.010 passed the following tests
Test: run cts-on-gsi -m CtsLiblogTestCases --skip-preconditions
Change-Id: I9bfca1522e90ebb68e6cecbdb63e3b67248e47c4
Signed-off-by: Xinghua Yang <xinghua.yang@mediatek.com>