Use RECOVERY_PRE_COMMAND before calling __reboot() recovery

For the Power menu,
frameworks/base/core/jni/android_os_Power.cpp#L180
already uses RECOVERY_PRE_COMMAND if
TARGET_RECOVERY_PRE_COMMAND is defined in the
BoardConfig.mk for a device to make a system() call before
calling __reboot() for recovery. This commit adds
the same thing to the other places that we know we are
getting into recovery using __reboot(), namely,
adb reboot recovery, the reboot binary and init
in the case of errors.

Change-Id: If0a9c7f22de2aa187c921b60ad5edd77b49e095d
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

Conflicts:

	libcutils/android_reboot.c
RECOVERY_PRE_COMMAND_CLEAR_REASON and extended reboot arguments

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

Allow also to override toolbox reboot applet, for bootmenu

Change-Id: I975af19a8f295d1e341c7433f96f669db611f89c