Allow dynamic uiautomator test jars and classes.

Currently UiAutomatorTest requires the jar artifact paths and test classes to
be specified when command is run. This is non ideal for situations where the
jar artifact name is not known until build is retrieved.

This CL corrects that by:
  - adds API to BuildInfo to retrieve arbitrary files.
  - Add installer that pushes all .jars found in build to device
  - Adapt UIAutomatorTest to build the jar classpath dynamically from
device contents
  - Make specifying classes optional, since the uiautomator runner on device
can now find them dynamically

Also made an unrelated fix where the run name reported by UiAutomatorTest was
always null.

Bug 8024777, 7742378

Change-Id: Ie4a1ab170f2fed8a64c6e43817e62b21c3c8bd68
7 files changed