Tests: prerequisites checking reworked.

Prerequisites check moved to the module level to simplify class structure.
Discovery and prerequisites checks functions moved to the separate files.
Introduced "require" fixture to provide per-test requirements check.

test/test_java_isolation_rootfs.py

@@ -5,15 +5,12 @@ import pytest
 from unit.applications.lang.java import TestApplicationJava
 from unit.option import option
 
+prerequisites = {'modules': {'java': 'all'}, 'privileged_user': True}
+
 
 class TestJavaIsolationRootfs(TestApplicationJava):
-    prerequisites = {'modules': {'java': 'all'}}
-
     @pytest.fixture(autouse=True)
-    def setup_method_fixture(self, is_su, temp_dir):
-        if not is_su:
-            pytest.skip('require root')
-
+    def setup_method_fixture(self, temp_dir):
         os.makedirs(f'{temp_dir}/jars')
         os.makedirs(f'{temp_dir}/tmp')
         os.chmod(f'{temp_dir}/tmp', 0o777)
@@ -35,10 +32,7 @@ class TestJavaIsolationRootfs(TestApplicationJava):
         except subprocess.CalledProcessError:
             pytest.fail("Can't run mount process.")
 
-    def teardown_method(self, is_su):
-        if not is_su:
-            return
-
+    def teardown_method(self):
         try:
             subprocess.run(
                 ["umount", "--lazy", f"{option.temp_dir}/jars"],
@@ -51,13 +45,8 @@ class TestJavaIsolationRootfs(TestApplicationJava):
         except subprocess.CalledProcessError:
             pytest.fail("Can't run umount process.")
 
-    def test_java_isolation_rootfs_chroot_war(self, is_su, temp_dir):
-        if not is_su:
-            pytest.skip('require root')
-
-        isolation = {
-            'rootfs': temp_dir,
-        }
+    def test_java_isolation_rootfs_chroot_war(self, temp_dir):
+        isolation = {'rootfs': temp_dir}
 
         self.load('empty_war', isolation=isolation)