clingo: don't skip tests that deal with file permissions

When we first merged the ASP-based solver, unit-tests
were run in a Docker container with root permissions
and that was preventing a few tests to succeed.

Since some time though, clingo is tested as a regular
user within Github Actions VMs, so we should start to
run checks again.

lib/spack/spack/test/cmd/buildcache.py

@@ -125,10 +125,6 @@ def test_buildcache_create_fails_on_noargs(tmpdir):
         buildcache('create', '-d', str(tmpdir), '--unsigned')
 
 
-@pytest.mark.skipif(
-    os.environ.get('SPACK_TEST_SOLVER') == 'clingo',
-    reason='Test for Clingo are run in a container with root permissions'
-)
 def test_buildcache_create_fail_on_perm_denied(
         install_mockery, mock_fetch, monkeypatch, tmpdir):
     """Ensure that buildcache create fails on permission denied error."""

lib/spack/spack/test/database.py

@@ -638,10 +638,6 @@ def test_090_non_root_ref_counts(mutable_database):
     assert mpich_rec.ref_count == 0
 
 
-@pytest.mark.skipif(
-    os.environ.get('SPACK_TEST_SOLVER') == 'clingo',
-    reason='Test for Clingo are run in a container with root permissions'
-)
 def test_100_no_write_with_exception_on_remove(database):
     def fail_while_writing():
         with database.write_transaction():
@@ -659,10 +655,6 @@ def fail_while_writing():
         assert len(database.query('mpileaks ^zmpi', installed=any)) == 1
 
 
-@pytest.mark.skipif(
-    os.environ.get('SPACK_TEST_SOLVER') == 'clingo',
-    reason='Test for Clingo are run in a container with root permissions'
-)
 def test_110_no_write_with_exception_on_install(database):
     def fail_while_writing():
         with database.write_transaction():

lib/spack/spack/test/llnl/util/lock.py

@@ -661,10 +661,6 @@ def test_upgrade_read_to_write(private_lock_path):
     assert lock._file is None
 
 
-@pytest.mark.skipif(
-    os.environ.get('SPACK_TEST_SOLVER') == 'clingo',
-    reason='Test for Clingo are run in a container with root permissions'
-)
 def test_upgrade_read_to_write_fails_with_readonly_file(private_lock_path):
     """Test that read-only file can be read-locked but not write-locked."""
     # ensure lock file exists the first time