Installer: Use nanoTime instead of currentTimeMillis

It is possible for the Installer to timeout even though the elapsed
time of 100,000 ms has not elapsed.  This can happen if the system
clock changes while we are running something from the Installer.

The documentation says not to use currentTimeMillis for determining
timeouts and recommends using nanoTime() instead.

Change-Id: I376d5b0fad8eefcdeabbb7ed89ebd3d1d3c96ba0