Add new option to allow lease reductions

The current prolong-for option allows to increment/prolong the
duration of lease by passing a parameter. It could also allow to
reduce the lease duration, but the parameter needs to be passed in
a way that is unclear for the user (for example, --prolong-for " -1d")

With this fix we added a new option to allow lease duration reductions
with a similar option to the "prolong-for".
Both options are mutually exclusive

Change-Id: Ifa616b8d215ed2825f98bea64ce8419866d252d5
Closes-Bug: #1305129
Merge "Add new option to allow lease reductions"