cli: Format the hostname column properly in the 'pool list' o/p

In the pool list output, if the hostname is lengthier, then the indentation was not proper.

Solution:
1) get the full list of hostnames first (prior to display)
2) Determine the maximum length of the hostname strings from that
3) Create an appropriate display padding amount, using the length from (2)

Change-Id: Icc3724975a5e30b02b8e06db709930cbac5e0875
BUG: 1028871
Signed-off-by: Vijaikumar M <vmallika@redhat.com>
Reviewed-on: http://review.gluster.org/8127
Tested-by: Justin Clift <justin@gluster.org>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Atin Mukherjee <amukherj@redhat.com>
Reviewed-by: Avra Sengupta <asengupt@redhat.com>
Reviewed-by: Rajesh Joseph <rjoseph@redhat.com>
Reviewed-by: Kaushal M <kaushal@redhat.com>