recovery: Properly detect userdebug or eng builds

The recovery system behaves a little bit differently on userdebug or
eng builds by presenting error reports to the user in the ui.
This is controlled by checking the build fingerprint for the string
:userdebug/ or :eng/. But with AOSP version numbers most AOSP
builds blows the 92 char limit of ro.build.fingerprint and therefore
the property is not set, so this condition will always be evaluated
to false, for most builds.

Instead of depending on the flaky ro.build.fingerprint this change
uses ro.debuggable.

Change-Id: I74bc00c655ac596aaf4b488ecea58f0a8de9c26b