libcutils : reboot mount fix

On aries for eg, cache needs to be rw for the RECOVERY_PRE_COMMAND to
work because we write to /cache/.startrecovery

This patchset moves the RECOVERY_PRE_COMMAND prior to the remount.

Change-Id: Iab1da9a15e64e8831b04e4eb21d824de5f8bd0eb
RECOVERY_PRE_COMMAND_CLEAR_REASON and extended reboot arguments

fix the 2 new warnings created by our 4-lines recovery patch ;p

Change-Id: I975af19a8f295d1e341c7433f96f669db611f89c