support package scope prepare/teardown

* introduced concept of module test config as AndroidTest.xml;
  for now target preparers can be defined in it to complete tasks
  before and after (CTS) package scope test execution
* modified CtsTest to invoke the preparers around package scope
  test execution
* modified related makefiles to "install" the module test config
  into CTS repository/testcases
* default common test config that included the commonly useful
  preparers
* modified accessibility tests to adopt module test config

Bug: 19442125

Change-Id: I1c694997c96c37150399395de2fbc464264c2aba