Revert "Revert "Some cleanups to recovery.""

This reverts commit 8584fcf6.

This CL re-lands commit c0319b60.
The "stage" and "reason" variables are now declared as global by
dropping the static qualifier, because they may be used by vendor
recovery libraries.

Test: lunch aosp_angler-userdebug; mmma bootable/recovery
Test: lunch aosp_dragon-userdebug; mmma bootable/recovery

Change-Id: I252c346f450079478cff22bbff01590b8ab2e2b3