update stdlib requirement to 4.2.0

puppetlabs-tomcat makes use of delete_undef_values(), which appeared in puppetlabs-stdlib 4.2.0.
Updated dependency module names in metadata.json to remove missing dependency warnings on 'puppet module list'
Directory in opt should only be created if is true

Directory in opt should only be created if the boolean
$install_from_source is true.

Validate and manage boolean for install_from_source var and make the test succeed

Update README.md and instance.pp in order to reflect new behaviour on
Merge branch 'master' of https://github.com/krionux/puppetlabs-tomcat