Fix errno checking for dalvik-cache creation.

On the host, it's possible for /tmp/foo/dalvik-cache/<isa> to
not exist, but for /tmp/foo/dalvik-cache to be already present.
In this scenario, the first mkdir() can fail with EEXIST.

(cherry picked from commit 6fa28aef)

Change-Id: I1da79ad23a4ff510a0f87eca4b52d9f52ab791ad