Update to new test runner and espresso.

test runner 0.6-alpha and espresso 2.6-alpha have fixed the issue
with broken @UIThreadTest annotation. This change moves support
library to use these versions.

Bug: 29547049
Change-Id: I3d53e2594871461d4f293713a3637395afc43d3e
diff --git a/build.gradle b/build.gradle
index 291dac2..38a308e 100644
--- a/build.gradle
+++ b/build.gradle
@@ -36,6 +36,9 @@
 ext.buildToolsVersion = '23.0.2'
 ext.buildNumber = Integer.toString(ext.extraVersion)
 
+ext.testRunnerVersion = '0.6-alpha'
+ext.espressoVersion = '2.3-alpha'
+
 // Enforce the use of prebuilt dependencies in all sub-projects. This is
 // required for the doclava dependency.
 ext.usePrebuilts = "true"