Cherry-pick to 6.0.x: Fix: indented keywords would fail template expansion

There's a limitation / bug in templates that they cannot be parsed if they contain indented keywords

Forum link where this issue was discussed: http://drools.46999.n3.nabble.com/Fwd-drools-Fixing-issue-where-indented-keywords-would-fail-template-expansion-170-td4021476.html   


This is already fixed in 5.5.x by pull request https://github.com/droolsjbpm/drools/pull/170


This new pull request proposes to cherry-pick this fix to 6.0.x