Fixes for DPCTLService_InitLogger

Replaced use of `stat` function with use of `filesystem::is_directory`.
Stat was always erroring out even for path to existing directory.

Created `dpctl._dev` module for developers. It adds

```python
dpctl._dev.init_logger(log_dir=None)
```

Function to initialize the logger. It uses `"dpctl"` for application name,
and supplied log directory. `log_dir=None` is interpreted as use the current
working directory.

```pyton
dpctl._dev.fini_logger()
```

Call ShutdownLogger.

```python
dpctl._dev.verbose(verbostiy="warning", log_dir=None)
```

Context manager which initializes the logger, and sets the verbosity level
for a given block of Python code:

Example:

```
In [1]: import dpctl, dpctl._dev as dd

In [2]: with dd.verbose(): dpctl.SyclDevice().parent_device
No parent for device because it is not a subdevice -33 (CL_INVALID_DEVICE) in DPCTLDevice_GetParentDevice at /localdisk/work/opavlyk/repos/dpctl/libsyclinterface/source/dpctl_sycl_device_interface.cpp:540

In [3]: dpctl.SyclDevice().parent_device  # no message

In [4]: with dd.verbose(): dpctl.SyclDevice().parent_device
No parent for device because it is not a subdevice -33 (CL_INVALID_DEVICE) in DPCTLDevice_GetParentDevice at /localdisk/work/opavlyk/repos/dpctl/libsyclinterface/source/dpctl_sycl_device_interface.cpp:540

In [5]: dpctl.SyclDevice().parent_device  # no message

In [6]: quit
```

Author: oleksandr-pavlyk

dpctl/_dev.pyx

@@ -0,0 +1,77 @@
+#                      Data Parallel Control (dpctl)
+#
+# Copyright 2020-2021 Intel Corporation
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# distutils: language = c++
+# cython: language_level=3
+# cython: linetrace=True
+
+""" Implements developer utilities.
+"""
+import contextlib
+import os
+
+
+cdef extern from "syclinterface/dpctl_service.h":
+   cdef void DPCTLService_InitLogger(const char *, const char *)
+   cdef void DPCTLService_ShutdownLogger()
+
+
+def init_logger(log_dir=None):
+    """Initialize logger to use given directory to save logs.
+
+    The call has no effect if `dpctl` was not built to use logger.
+    """
+    cdef bytes p = b""
+    cdef const char *app_name = "dpctl"
+    if log_dir is None:
+        log_dir = os.getcwd()
+    if not os.path.exists(log_dir):
+        raise ValueError(f"Path {log_dir} does not exist")
+    if isinstance(log_dir, str):
+        p = bytes(log_dir, "utf-8")
+    else:
+        p = bytes(log_dir)
+    DPCTLService_InitLogger(app_name, <char *>p)
+
+
+def fini_logger():
+    """Finilize logger.
+
+    The call has no effect if `dpctl` was not built to use logger.
+    """
+    DPCTLService_ShutdownLogger()
+
+
+@contextlib.contextmanager
+def verbose(verbosity="warning", log_dir=None):
+    """Context manager that activate verbosity"""
+    _allowed_verbosity = ["warning", "error"]
+    if not verbosity in _allowed_verbosity:
+        raise ValueError(
+            f"Verbosity argument not understood. "
+            f"Permitted values are {_allowed_verbosity}"
+        )
+    init_logger(log_dir=log_dir)
+    _saved = os.environ.get("DPCTL_VERBOSITY", None)
+    os.environ["DPCTL_VERBOSITY"] = verbosity
+    try:
+        yield
+    finally:
+        fini_logger()
+        if _saved:
+            os.environ["DPCTL_VERBOSITY"] = _saved
+        else:
+            del os.environ["DPCTL_VERBOSITY"]

libsyclinterface/source/dpctl_service.cpp

@@ -30,8 +30,8 @@
 #include <algorithm>
 #include <cstring>
 #include <iostream>
-#include <sys/stat.h>
 #ifdef ENABLE_GLOG
+#include <filesystem>
 #include <glog/logging.h>
 #endif
 
@@ -50,8 +50,12 @@ void DPCTLService_InitLogger(const char *app_name, const char *log_dir)
     google::InstallFailureSignalHandler();
     FLAGS_colorlogtostderr = true;
     FLAGS_stderrthreshold = google::FATAL;
-    struct stat buffer;
-    if (stat(log_dir, &buffer) != 0) {
+
+    namespace fs = std::filesystem;
+    const fs::path path(log_dir);
+    std::error_code ec;
+
+    if (fs::is_directory(path, ec)) {
         FLAGS_log_dir = log_dir;
     }
     else {