Deliver example settings.xml & essential updates for older salt versions

[noelmcloughlin]

This PR adds an example maven-setttings.xml file to the formula. Maven is quite useless without settings.xml file anyway so this is useful starting point for future idea here. The Jinja template example requires end-user to update two variables in settings.sls.

This PR addresses following issues seen when tested on older Salt version-

1. Salt 2015.8.8 (Beryllium) generates "Requisite declaration XXXXXXXXXXX in SLS sqlplus is not formed as a single key dictionary" errors on requires-

      Solution: Prefix requisite-type to all requires (i.e. - **cmd**: download-maven-archive ).

2. . Salt generates warnings on Fedora regarding saltstack/salt#39751

      Solution: Remove "user: root" and "group: root" from archive.extracted state.

3. Source_hash handling has issues in salt 2016.11.0 and earlier.

    Solution: Only check source_hash on newer Salt version as interim measure. Twooster on #salt IRC suggested "{% if grains['saltversioninfo'] <= [2016, 11, 6] %}" to workaround version-check issue on opensuse/salt 2016.3.

4. On older Salt version the formula is broken as archive.extracted "name" exists.

   Solution: Reintroduce "if_missing" parameter to archive.extracted as recommended solution for older Salt.  This fixes formula on old Salt.

5. Getting "recursive requisite" error on fedora/ubuntu for statename {{ xxxxx }}

   Solution: Seemingly fixed by renaming state to avoid ID clash- -{{ archive_file }}: +maven-remove-prev-archive:

6. Bug in maven.env state: https://github.com/saltstack-formulas/maven-formula/issues/14

   Solution: Fixed in this PR

Tested successfuly (no pillars):

• Fedora 25 / Salt 2016.11.3.1.fc25
• Ubunutu 17 / Salt 2017.7.0+ds-1
• Opensuse Leap / Salt 2016.3.4.84.13

[whiteinge]

This looks good to me. 👍 Especially since this fixes some breakages. Thanks!

[noelmcloughlin]

Thanks @whiteinge appreciated.