Print used adb version

Helps with debugging flakes.

Test: ./art/tools/buildbot-setup-device.sh
Change-Id: Iddbfb2499242529872e12d3553dedf927e2c020f
diff --git a/tools/buildbot-setup-device.sh b/tools/buildbot-setup-device.sh
index decb247..811ba80 100755
--- a/tools/buildbot-setup-device.sh
+++ b/tools/buildbot-setup-device.sh
@@ -26,6 +26,7 @@
 fi
 
 # Setup as root, as some actions performed here require it.
+adb version
 adb root
 adb wait-for-device