Handle user consent denial sooner

Currently dumpstate prompts the user for consent rightaway when called
via the API, but does not check for the result until the entire
bugreport is generated. This can make for a poor user experience - for
e.g. the client will continue to show a progress bar for a long time
after user denied consent.

Fix by checking for user consent intermittently.

BUG: 128270426
Test: Tested canceling during each long running operation in internal
Test: bugreport from power menu (ie non-api flow) still works as
expected
Test: adb shell
/data/nativetest64/dumpstate_smoke_test/dumpstate_smoke_test &&
adb shell /data/nativetest64/dumpstate_test/dumpstate_test

Change-Id: Icbed7c510ff9c9a882a7b49eac1a92fa17727635
Merged-In: Icbed7c510ff9c9a882a7b49eac1a92fa17727635