Prepare tempest-slow-parallel job and run periodically

tempest-slow-py3 job run all the slow test serially which
takes lot of time and end up job timeout. This preparing
tempest-slow-parallel job which will run slow tests parallelly
in periodic run. Based on the results, later we can make
tempest-slow-py3 job to run tests in parallel.

Also, run tempest-full-parallel in periodic and based on the
result we can run tempest-full-py3 job scenario tests in parallel.

Relavant-Bug: #2004780

Change-Id: I876dacb40daa384cddc8faae3200cd3d39506ddc
diff --git a/tox.ini b/tox.ini
index e1c17df..d5b41af 100644
--- a/tox.ini
+++ b/tox.ini
@@ -289,6 +289,18 @@
     find . -type f -name "*.pyc" -delete
     tempest run --serial --regex {[testenv:slow-serial]regex} {posargs}
 
+[testenv:slow]
+envdir = .tox/tempest
+sitepackages = {[tempestenv]sitepackages}
+basepython = {[tempestenv]basepython}
+setenv = {[tempestenv]setenv}
+deps = {[tempestenv]deps}
+# The regex below is used to select the slow tagged tests:
+regex = '\[.*\bslow\b.*\]'
+commands =
+    find . -type f -name "*.pyc" -delete
+    tempest run --regex {[testenv:slow]regex} {posargs}
+
 [testenv:ipv6-only]
 envdir = .tox/tempest
 sitepackages = {[tempestenv]sitepackages}