AppTransitionTests to launch apps

Apps and launch iterations are configurable during the test.
Capturing atrace during the launch is optional.

Bug 28793299

Sample test commands

am instrument -w  -e class com.android.apptransition.tests.AppTransitionTests#testColdLaunchFromHome -e launch_apps "Gmail|Maps"
-e launch_iteration 2 -e postlaunch_timeout 5000 -e trace_directory sdcard com.android.apptransition.tests/android.support.test.runner.AndroidJUnitRunner

am instrument -w  -e class com.android.apptransition.tests.AppTransitionTests#testHotLaunchFromHome -e launch_apps "Gmail|Maps"
-e launch_iteration 2 -e postlaunch_timeout 5000 -e trace_directory sdcard com.android.apptransition.tests/android.support.test.runner.AndroidJUnitRunner

am instrument -w  -e class com.android.apptransition.tests.AppTransitionTests#testAppToRecents -e pre_launch_apps
"Calculator|Clock|Settings|Downloads|Contacts|Phone|Gmail|Maps" -e launch_apps "Gmail|Chrome" -e launch_iteration 2 -e
postlaunch_timeout 5000  -e trace_directory sdcard com.android.apptransition.tests/android.support.test.runner.AndroidJUnitRunner

am instrument -w  -e class com.android.apptransition.tests.AppTransitionTests#testHotLaunchFromRecents
-e pre_launch_apps "Calculator|Clock|Settings|Downloads|Contacts|Phone|Gmail|Maps" -e launch_apps "Gmail|Chrome"
-e launch_iteration 2 -e postlaunch_timeout 5000  -e trace_directory sdcard com.android.apptransition.tests/android.support.test.runner.AndroidJUnitRunner

Change-Id: If1d4a5cd3595bd4b076a4980e51c58f75f0c578b