Fix CtsShortcutHostTestCases#testSecondaryUser

This patch uses Instrumentation parameter inside
getDefaultLauncher function to obtain user ID
from it and get default launcher namely for that
user as setDefaultLauncher function sets launcher
for the user from Instrumentation context. This
fixes incorrect launcher settings for the cases
that use two sequential calls to get/set
default launcher.

Bug: 145774461
Test: run cts -m CtsShortcutHostTestCases -t \
android.content.pm.cts.shortcuthost.ShortcutManagerMultiuserTest#testSecondaryUser

Signed-off-by: Sergii Iegorov <sergii.iegorov@globallogic.com>
Change-Id: I8941f5648ad783c7681fdb56677e855756db957d