Make greenlet optional

The greenlet library is not always used. It is used to capture detail
of green threads but this part can be skipped in case greenlet is not
present.

Also eventlet in test requirements is not used and can be removed.

Change-Id: I57edfe4d975ce42ca92a9242d4b32e69d1cec268

oslo_reports/guru_meditation_report.py

@@ -75,6 +75,11 @@ from oslo_reports.generators import threading as tgen
 from oslo_reports.generators import version as pgen
 from oslo_reports import report
 
+try:
+    import greenlet
+except ImportError:
+    greenlet = None
+
 
 LOG = logging.getLogger(__name__)
 
@@ -240,8 +245,9 @@ class GuruMeditation(object):
         self.add_section('Threads',
                          tgen.ThreadReportGenerator(self.traceback))
 
-        self.add_section('Green Threads',
+        if greenlet:
-                         tgen.GreenThreadReportGenerator())
+            self.add_section('Green Threads',
+                             tgen.GreenThreadReportGenerator())
 
         self.add_section('Processes',
                          prgen.ProcessReportGenerator())

requirements.txt

@@ -4,5 +4,4 @@ oslo.serialization!=2.19.1,>=2.18.0 # Apache-2.0
 psutil>=3.2.2 # BSD
 oslo.i18n>=3.15.3 # Apache-2.0
 oslo.utils>=3.33.0 # Apache-2.0
-greenlet>=0.4.15 # MIT
 oslo.config>=5.1.0 # Apache-2.0

setup.cfg

@@ -22,6 +22,10 @@ classifier =
     Programming Language :: Python :: 3 :: Only
     Programming Language :: Python :: Implementation :: CPython
 
+[extras]
+greenlet =
+  greenlet>=0.4.15 # MIT
+
 [files]
 packages =
     oslo_reports

test-requirements.txt

@@ -3,7 +3,7 @@ oslotest>=3.2.0 # Apache-2.0
 stestr>=2.0.0 # Apache-2.0
 
 # for testing optional parts
-eventlet!=0.18.3,!=0.20.1,>=0.18.2 # MIT
+greenlet>=0.4.15 # MIT
 
 coverage!=4.4,>=4.0 # Apache-2.0