Improve setTtl command to take the time-to-live value with unit
Current setTtl command sets the time-to-live of a path in unit of ms.
This JIRA aims to improve it to take the time duration with a given unit.
e.g. instead of only supporting
One can take a look at alluxio.Configuration#getMs() method see how getMs() does the similar function to parse time with unit
Feature added and merged into master