Tests: get rid of classes in test files.

Class usage came from the unittest framework and it was always redundant
after migration to the pytest.  This commit removes classes from files
containing tests to make them more readable and understandable.

test/test_go_isolation_rootfs.py

@@ -1,5 +1,4 @@
-import pytest
-from unit.applications.lang.go import TestApplicationGo
+from unit.applications.lang.go import ApplicationGo
 
 prerequisites = {
     'modules': {'go': 'all'},
@@ -7,16 +6,14 @@ prerequisites = {
     'privileged_user': True,
 }
 
+client = ApplicationGo()
 
-class TestGoIsolationRootfs(TestApplicationGo):
-    def test_go_isolation_rootfs_chroot(self, temp_dir):
-        isolation = {'rootfs': temp_dir}
 
-        self.load('ns_inspect', isolation=isolation)
+def test_go_isolation_rootfs_chroot(temp_dir):
+    client.load('ns_inspect', isolation={'rootfs': temp_dir})
 
-        obj = self.getjson(url='/?file=/go/app')['body']
+    obj = client.getjson(url='/?file=/go/app')['body']
+    assert obj['FileExists'], 'app relative to rootfs'
 
-        assert obj['FileExists'], 'app relative to rootfs'
-
-        obj = self.getjson(url='/?file=/bin/sh')['body']
-        assert not obj['FileExists'], 'file should not exists'
+    obj = client.getjson(url='/?file=/bin/sh')['body']
+    assert not obj['FileExists'], 'file should not exists'