[entropy.misc, rigo] fix file-like objects with Python 3

FakeOutFile and LogFile need .buffer like Python 3 "text" file objects
which is needed when in rigo standard output/error is replaced, and then
it reaches Portage which does this:

	    if sys.hexversion >= 0x3000000 and fd in (sys.stdout, sys.stderr):
		    fd = fd.buffer
    fd.write(mystr)

(/usr/lib64/python3.6/site-packages/portage/util/__init__.py).

Entropy internal code did not need this.

Note, after this commit, changes done previously:
    1)
    commit 0869912ec4

	[entropy.spm] Rigo related Python 3 fix

	  File "/usr/lib64/python3.6/site-packages/entropy/spm/plugins/interfaces/portage_plugin/__init__.py", line 101, in _pusher
	    self._std.buffer.write(chunk)
	AttributeError: 'FakeOutFile' object has no attribute 'buffer'

    2)
    commit 8700aade27

	[entropy.spm, rigo] Rigo related Python 3 fixes

	1)
	  File "/usr/lib/python-exec/python3.6/RigoDaemon_app.py", line 362, in _pusher
	    fobj.write(chunk)
	TypeError: write() argument must be str, not bytes

	2)
	  File "/usr/lib64/python3.6/site-packages/entropy/spm/plugins/interfaces/portage_plugin/__init__.py", line 77, in __init__
	    self.buffer = Writer(self, self._std.buffer)
	AttributeError: 'FakeOutFile' object has no attribute 'buffer'

    (...)

could be likely reverted; not tested, it could be better to have them anyway to
avoid futher re/encoding/checks if conversions are needed (subjective).

Fixes bug 5899.

lib/entropy/misc.py

@@ -35,7 +35,8 @@ import threading
 from collections import deque
 
 from entropy.const import etpConst, const_isunicode, \
-    const_isfileobj, const_convert_log_level, const_setup_file
+    const_isfileobj, const_convert_log_level, const_setup_file, \
+    const_convert_to_unicode
 from entropy.exceptions import EntropyException
 
 import entropy.tools
@@ -1665,6 +1666,24 @@ class FastRSS(object):
         const_setup_file(self.__file, etpConst['entropygid'], 0o664)
 
 
+class FileobjCompatBuffer:
+
+    """
+    Compatibility shim for file object with the buffer attribute.
+    To be used with classes whose write method expect strings.
+    """
+
+    def __init__(self, parent):
+        self._parent = parent
+
+    def write(self, msg):
+        msg_str = const_convert_to_unicode(msg)
+        self._parent.write(msg_str)
+
+    def flush(self):
+        self._parent.flush()
+
+
 class LogFile:
 
     """ Entropy simple logging interface, works as file object """
@@ -1715,6 +1734,9 @@ class LogFile:
             LogFile.DATE_FORMAT))
         self.__logger.addHandler(self.__handler)
 
+        if const_is_python3():
+            self.buffer = FileobjCompatBuffer(self)
+
     def __enter__(self):
         """
         Just return self, configuration is done in __init__

rigo/RigoDaemon/app/RigoDaemon_app.py

@@ -79,7 +79,7 @@ from entropy.exceptions import DependenciesNotFound, \
     EntropyPackageException, InterruptError, RepositoryError
 from entropy.i18n import _
 from entropy.misc import LogFile, ParallelTask, TimeScheduled, \
-    ReadersWritersSemaphore
+    ReadersWritersSemaphore, FileobjCompatBuffer
 from entropy.fetchers import UrlFetcher, MultipleUrlFetcher
 from entropy.output import TextInterface, purple, teal
 from entropy.client.interfaces import Client
@@ -340,6 +340,10 @@ class FakeOutFile(object):
         self._app_mgmt_mutex = app_mgmt_mutex
         self._app_mgmt_notes = app_mgmt_notes
         self._rfd, self._wfd = os.pipe()
+
+        if const_is_python3():
+            self.buffer = FileobjCompatBuffer(self)
+
         task = ParallelTask(self._pusher)
         task.name = "FakeOutFilePusher"
         task.daemon = True