liblog: retry -ENOTCONN | -ECONNREFUSED | -ENOENT indefinitely

Deal with recovering after transitory failures surrounding logd
crash or recovery.  Improve the chances that the logging functions
can work in a signal handler, not officially supported, but making
sure logging is not blamed for system lockups when misused.

Reorder gTests so that setuid(AID_SYSTEM) is performed after
liblog.enoent test, and that this occurs after other tests that
like to see buffers with content in them as we stop logd.

Test: gTest liblog-unit-tests --gtest_filter=liblog.enoent
Bug: 33755074
Change-Id: I66f88599534614b7b61da6b2ae5fe099ebaced3a