test: conditional metrics roles reload skip

Before this patch, tests were marked with xfail since there was a bug in
metrics module [1]. This bug is fixes in newer versions, so xfail is
replaced with skip based on metrics version.

1. tarantool/metrics#334

Follows #244

test/helper.lua

@@ -553,4 +553,18 @@ function helpers.complement_tuples_batch_with_operations(tuples, operations)
     return tuples_operation_data
 end
 
+function helpers.is_metrics_0_12_0_or_older()
+    local metrics = require('metrics')
+
+    -- metrics 0.13.0 introduced VERSION, but it is likely to be deprecated in the future:
+    -- https://github.com/tarantool/metrics/commit/a7e666f50d23c3e1a11b9bc9882edddec2f4c67e
+    -- metrics 0.16.0 introduced _VERSION which is likely going to replace VERSION:
+    -- https://github.com/tarantool/metrics/commit/8f9b667f9db59ceff8e5d26e458244e2d67838da
+    if (metrics.VERSION == nil) and metrics._VERSION == nil then
+        return true
+    end
+
+    return false
+end
+
 return helpers

test/integration/stats_test.lua

@@ -772,7 +772,8 @@ pgroup.before_test(
     generate_stats)
 
 pgroup.test_role_reload_do_not_reset_observations = function(g)
-    t.xfail_if(g.params.args.driver == 'metrics',
+    t.skip_if((g.params.args.driver == 'metrics')
+        and helpers.is_metrics_0_12_0_or_older(),
         'See https://github.com/tarantool/metrics/issues/334')
 
     local stats_before = get_stats(g)
@@ -1084,7 +1085,8 @@ group_metrics.before_test(
     generate_stats)
 
 group_metrics.test_role_reload_do_not_reset_metrics_observations = function(g)
-    t.xfail('See https://github.com/tarantool/metrics/issues/334')
+    t.skip_if(helpers.is_metrics_0_12_0_or_older(),
+        "See https://github.com/tarantool/metrics/issues/334")
 
     helpers.reload_roles(g.cluster:server('router'))
     g.router:eval("crud = require('crud')")