Fix map usage on py3 in v2 test_volumes_snapshots_list

This commit fixes the usage around map in
test_snapshot_list_param_marker(). In py2 map() returns a list, but in
py3 map() returns an map iterator. To work around this difference simply
use a list comprehension instead.

Change-Id: I0219ee7ac35d7389263af67eb0dde2b0f96ea22f
1 file changed