Make sure correct default values for ActivityStarter.

Request#reset() used different default values for the calling uid
and pid. Since reset is called before use, these the default values
were incorrect.

This changelist corrects this issue.

Change-Id: I1a04ed443fb5d9d6b248bbb1b2031d87f83f9774
Fixes: 70507511
Test: atest OsHostTests#testNonExportedActivities