Add hosts data source

[ddelnano]

This is a continuation of #120

Todo

• [x] ~Update the data sources id to be a hash of the parameters to prevent collisions~ - the current implementation should be fine for now
• [x] ~Add check for length of pool variable to prevent multiple pools matching~ - not necessary since the the lookup is by pool id (so guaranteed to fail or be a single result)
• [x] Fix TestAccXenorchestraDataSource_host test (the required id attribute is causing it to fail)
• [x] Consolidate xoa/data_source_host.go and xoa/host.go
• [x] Brainstorm ideas on how to increase coverage on TestGetSortedHosts and the acceptance tests (testing that sorting works, etc) - Verify that number of hosts in acceptance test is greater than 1 and create a new TestCheckTypeListAttrSorted to validate the sorting is correct
• [x] Create GitHub issue to allow server side filtering to include tags and other attributes - #143
• [x] Add documentation for the data source
• [x] make testacc passes (currently all new tests are passing)

[ddelnano]

@gohumble I made additions on top of your changes in #142. The largest changes were around improving the acceptance tests to verify that the sorting works.

This should be done aside from the docs that need to be written but I'd appreciate it if you could give this a review.

[gohumble]

sorry for replying bit late. tested your changes in my home lab. everything is still looking good :)

[brd]

Is it worth doing a release with these changes in?

[ddelnano]

@brd I will. I'm trying to merge #144 before making the next release.

[ddelnano]

@brd it's now available in v0.19.0 of the provider