tox: update python to python3

Changes:
    - Point the python to python3 env

Tested:
    - tox currently does not seems to work with
      latest python version.
Change-Id: I6556071a6de2e72fcf971356ad816038f1cbe292
Signed-off-by: George Keishing <gkeishin@in.ibm.com>
diff --git a/tox.ini b/tox.ini
index 5b27dc6..211e78e 100644
--- a/tox.ini
+++ b/tox.ini
@@ -25,7 +25,7 @@
 setenv = {[testenv]setenv}
 commands =
     {[testenv]commands}
-    python -m robot.run --argumentfile {env:ARG_FILE} {posargs}
+    python3 -m robot.run --argumentfile {env:ARG_FILE} {posargs}
 
 
 [testenv:palmetto]
@@ -34,7 +34,7 @@
     OPENBMC_MODEL=./data/Palmetto.py
 commands =
     {[testenv]commands}
-    python -m robot.run --argumentfile {env:ARG_FILE} {posargs}
+    python3 -m robot.run --argumentfile {env:ARG_FILE} {posargs}
 
 
 [testenv:qemu]
@@ -43,7 +43,7 @@
     OPENBMC_MODEL=./data/Palmetto.py
 commands =
     {[testenv]commands}
-    python -m robot.run --argumentfile {env:ARG_FILE} {posargs}
+    python3 -m robot.run --argumentfile {env:ARG_FILE} {posargs}
 
 
 [testenv:witherspoon]
@@ -52,7 +52,7 @@
     OPENBMC_MODEL=./data/Witherspoon.py
 commands =
     {[testenv]commands}
-    python -m robot.run --argumentfile {env:ARG_FILE} {posargs}
+    python3 -m robot.run --argumentfile {env:ARG_FILE} {posargs}
 
 [testenv:romulus]
 deps     = {[testenv]deps}
@@ -60,4 +60,4 @@
     OPENBMC_MODEL=./data/Romulus.py
 commands =
     {[testenv]commands}
-    python -m robot.run --argumentfile {env:ARG_FILE} {posargs}
+    python3 -m robot.run --argumentfile {env:ARG_FILE} {posargs}