This commit reduce the number of I/O done by the swift-object-relinker.
First, it saves a progress state of relinking and cleanup in case the
process is interrupted during the operation. This allow to resume
operation without rescanning all partitions.
Secondly, it prevents from being scanned by relink and cleanup all
partitions that are bigger than 2^part_power (or (2^next_part_power)/2).
These partitions were not existing before the beginning of the part_power
increase, so there is nothing to relink or cleanup.
Thirdly, it reverse-orders the partitions to scan so that some useless
work is avoided. If a device contains partitions 1 and 3, relinking
partition 1 will create "new" objects in partition 3, that will need to
be scanned when the relinker will work on partition 3. It is useless. If
partition 3 is done first, it will only contain the objects that need to
be relinked.
Fourthly, it allows to specify a unique device to work on.
To do that, some hooks were added in audit_location_generator to allow
to execute some custom code before/after iterating a
device/partition/suffix/hash.
Change-Id: If1bf8ed9036fb0ec619b0d4f16061a81a1af2082
3061ec803f