Allow entering rescue mode via recovery UI.

Only enabled on debuggable builds.

Bug: 128415917
Test: Sideload package on taimen.
Test: Choose "Enter rescue" from recovery UI.
Change-Id: I913dbdbcffd3179e6fa72ca862f74ca8f1364b02
Merged-In: I913dbdbcffd3179e6fa72ca862f74ca8f1364b02
(cherry picked from commit c6dc325e)