Make encryption configurable

Delay mounting encryptable but unencrypted volumes until we can
check the ro.vold.forceencrypt flag, then optionally encrypt.

Requires matching vold change from
    https://googleplex-android-review.git.corp.google.com/#/c/615309/

Bug: 18764230
Change-Id: If22008be8de6a4f3216b349f81ace49be1730314
diff --git a/rootdir/init.rc b/rootdir/init.rc
index cbcb842..e90acee 100644
--- a/rootdir/init.rc
+++ b/rootdir/init.rc
@@ -572,7 +572,7 @@
     # encryption) or trigger_restart_min_framework (other encryption)
 
 # One shot invocation to encrypt unencrypted volumes
-service encrypt /system/bin/vdc --wait cryptfs enablecrypto inplace default
+service encrypt /system/bin/vdc --wait cryptfs maybeenabledefaultcrypto
     disabled
     oneshot
     # vold will set vold.decrypt to trigger_restart_framework (default