[DO NOT MERGE] Notify vold when to start fstrim.

Since using the discard option for mounting an Ext4 file system
could lead to unpredictable slowdowns of I/O we will explicitly
control when to perform fstrim, i.e. discard unused blocks of the
mounted volume. We are using the idle maintenance intents sent by
the system which specify a window that one can use to perform
expensive maintenance tasks while the user does not use the device.

This change is adding a broadcast receiver for the idle maintenance
start intent to the mount services which then notifies vold when to
start fstrim.

Since fstrim will be run on a daily basis we do not expect fstrim
to be too long, so it is not interruptible. We will implement
interruption only in case we see issues.

bug:8056794

Change-Id: I1438479d2956b61b82d3a130854376f7a144aaf3
It helps to catch the right exception.

Bug: 7238149
Change-Id: I7b60ec44d1d1d5ece8a871cb089f811b611f4a4a
Adding idle maintenance service.

It is beneficial that there is a mechanism on the platform
to notify applications whether it is safe to perform somehow
expensive operations while the user is not using the device.
Thus, user experience will not be degraded. An example is
discarding of unused blocks on a mounted file system instead
of doing this on every write operation.

bug:8056794

Change-Id: I708bad9d3ce6c8f1d5a1c05c0abf46f81a3d464b

Conflicts:
	services/java/com/android/server/SystemServer.java
Perform idle maintenance when the device is charging.

Added the precondition that the device should be charging to the
existing ones of the device not being used for awhile and the
battery level being high enough. Note that even if the device is
charging, we have to check the battery level since the user can
unplug it at any time.

bug:8688454

Change-Id: I709b1620571301743dc3504a6a625e2018951bfa

Conflicts:
	services/java/com/android/server/EventLogTags.logtags
Removing a debug check when logging fstrim events.

This change is removing the check for debuggable build to
log fstrim events. While this was done everywhere else, one
place was overlooked.

bug:8688454

Change-Id: I354e1deebfd801f971dd91b9e7972c6ebfd093f3