cli/snapshot : gluster volume info should not show the options which are not set explicitly.

Problem : Even though snap-max-hard-limit, snap-max-soft-limit and
auto-delete values were not set explicitly, It was getting showed
in the output of gluster volume info.

Solution : Check if the value is already present in dictionary
(That means, it is set), If value is not present then consider
the default value,

NOTE : This patch doesn't solve the problem where the values
which is set globally are being displayed in gluster volume info

Change-Id: I61445b3d2a12eb68c38a19bea53b9051ad028050
BUG: 1145020
Signed-off-by: Sachin Pandit <spandit@redhat.com>
Reviewed-on: http://review.gluster.org/8191
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: Raghavendra Bhat <raghavendra@redhat.com>
Reviewed-by: Kaushal M <kaushal@redhat.com>
Signed-off-by: Sachin Pandit <spandit@redhat.com>
Reviewed-on: http://review.gluster.org/8793
Reviewed-by: Vijaikumar Mallikarjuna <vmallika@redhat.com>