Change keystone/gunicorn worker class from eventlet to threaded

Process scheduling data has showed that the threaded worker type is
9 to 10% more CPU efficient than the eventlet worker type.

This change sets gthread as worker type and sets the number of threads
to 2.

Test plan:

PASS: Run a full build, install, bootstrap and unlock.
PASS: Check alarms with 'fm alarm-list'
PASS: Install DC system with a subcloud. Fm alarm list.

Closes-Bug: 2083613

Change-Id: I8a83295dc67bf5ef62bafbcbd19fbf117f46f854
Signed-off-by: Rei Oliveira <Reinildes.JoseMateusOliveira@windriver.com>

openstack/keystone/debian/deb_patches/0001-Add-stx-support.patch

@@ -127,7 +127,7 @@ new file mode 100644
 index 000000000..de339caa6
 --- /dev/null
 +++ b/debian/stx/keystone-all
-@@ -0,0 +1,156 @@
+@@ -0,0 +1,157 @@
 +#!/bin/sh
 +# Copyright (c) 2013-2018 Wind River Systems, Inc.
 +#
@@ -167,7 +167,8 @@ index 000000000..de339caa6
 +###
 +EXEC="/usr/bin/gunicorn"
 +
-+WORKER="eventlet"
++WORKER="gthread"
++THREADS=2
 +# Increased timeout to facilitate large image uploads
 +TIMEOUT="200"
 +
@@ -220,9 +221,9 @@ index 000000000..de339caa6
 +
 +    start-stop-daemon --start --quiet --background --pidfile ${PIDFILE_PUBLIC} \
 +        --make-pidfile --exec ${PYTHON} -- ${EXEC} --bind ${BIND_PUBLIC} \
-+        --worker-class ${WORKER} --workers ${TIS_WORKERS} --timeout ${TIMEOUT} \
-+        --max-requests ${MAX_REQUESTS}  --max-requests-jitter ${MAX_REQ_JITTER_PUBLIC} \
-+        --log-syslog  \
++        --worker-class ${WORKER} --workers ${TIS_WORKERS} --threads ${THREADS} \
++        --timeout ${TIMEOUT} --max-requests ${MAX_REQUESTS} \
++        --max-requests-jitter ${MAX_REQ_JITTER_PUBLIC} --log-syslog  \
 +        --pythonpath '/usr/share/keystone' public:application --name keystone-public
 +
 +    RETVAL=$?