liblog: test report pmsg not configured if ENOMEM return

NB: bionic stdio is broken when providing appropriate errno value(s)
    on failure so libc.__pstore_append will not report pmsg
    misconfigured correctly on android for now.

Test: misconfigured kernel, watch for this message in liblog-unit-tests
Change-Id: Ifb1b550c7d3a3888000459c2f68c392cc23c379f