Add centos-src-build tox gate

Change-Id: Id8c8e0d4dcad62e3995fa7f2bb91b6bafb3a387c
Paritally-Implements: blueprint gate-source-builds

tox.ini

@@ -42,6 +42,22 @@ commands =
    sudo -g docker testr run ^(test_images).*
    bash -c "if [ -f buildconf.bak ]; then mv buildconf.bak .buildconf; fi"
 
+[testenv:images-centos-src]
+whitelist_externals = find
+                      bash
+                      sudo
+                      echo
+                      mv
+                      rm
+commands =
+   bash -c "if [ -f .buildconf ]; then mv .buildconf buildconf.bak; fi"
+   bash -c "echo PREFIX=centos-source- > .buildconf"
+   find . -type f -name "*.pyc" -delete
+   bash -c "if [ ! -d .testrepository ]; then testr init; fi"
+   sudo -g docker testr run ^(test_images).*
+   rm -f .buildconf
+   bash -c "if [ -f buildconf.bak ]; then mv buildconf.bak .buildconf; fi"
+
 [testenv:startenv]
 whitelist_externals = bash
 commands =