installd_service_test: fix ServiceTest.CreateAppDataSnapshot_ClearsCache

This test is failing on cf_x86_phone-userdebug target, with an error:
Failed copying /data/local/tmp/user_de/0/com.foo to /data/local/tmp/misc_de/0/rollback'

Logs shows that cp fails with "No such file or directory error":
02-05 08:37:49.444 12746 12746 I cp      : cp: /data/local/tmp/misc_de/0/rollback: No such file or directory
02-05 08:37:49.445 12746 12746 I cp      : cp terminated by exit(1)

Testcase is failing, because it doesn't create
/data/local/tmp/misc_de/0/rollback directory. It is hard to spot, because
other testcases in installd_service_test also create that directory, meaning
that depending on the order in which testcases are run,
CreateAppDataSnapshot_ClearsCache will either fail or succeed.

Verified that this is the case by running only
CreateAppDataSnapshot_ClearsCache testcase:
./data/nativetest/installd_service_test/installd_service_test --gtest_filter=*CreateAppDataSnapshot_ClearsCache*

Bug: 123631551
Fixes: 123631551
Test: ./data/nativetest/installd_service_test/installd_service_test --gtest_filter=*CreateAppDataSnapshot_ClearsCache*
Change-Id: I8277efe6076bac28fd07ea3705a21aae6b8cab14