making use of template file rather than a template string for ini file and few related fixes

Also adding 'bash' before run_test.sh since run_tests fails due to permission issue.
I had faced this sometimes where we would only need to change only a few parameters and would end creating a new testbed file altogether. 
I think it will be nice to have a method similar to getattr , but checks for env variable with same name first, then testbed, then assume a default.