Run tox in parallel and fix setup to use specific pyangbind version

Change-Id: I6f02f0137798c0d282550f8bbaa44cd499d4fefa
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>
diff --git a/tox.ini b/tox.ini
index f1cf7c9..ea045a8 100644
--- a/tox.ini
+++ b/tox.ini
@@ -29,6 +29,7 @@
 passenv = HOME
 deps =  -r{toxinidir}/requirements.txt
 skip_install = true
+parallel_show_output = true
 
 
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