Add logging around access calls.

We saw evidence, that the keystore exist method may be flaky. This
patch adds logging around the access calls used to check for key blobs.
Also adds a retry loop in case access return EAGAIN. (Although access
should not return EAGAIN).

Bug: 128318105
Test: Only logging added.
Change-Id: Ib07396f590c2f58e227f85869ada8c6d6dd46df4
1 file changed