Introduce PublicStemcells

Returns stemcells promoted by CI instead of the legacy ones at blob.cfblob.com

[#58381628]

Signed-off-by: Abhijit Hiremagalur <abhi@pivotallabs.com>
Add url to PublicStemcell

Postpone extracting to own file until PublicStemcellIndex and friends are gone.

[#58381628]

Signed-off-by: Abhijit Hiremagalur <abhi@pivotallabs.com>
Do not display public stemcell tags

Since the new location will not have any tags to display

[#58381628]
`bosh public stemcells` does not filter on --tags

Tags will no longer exist in new public stemcell location

[#58381628]
Move knowledge of tags inside PublicStemcellIndex

To make it look more like PublicStemcells

[#58381628]
Do not verify sha1 on public stemcell downloads

These will not be present in new public stemcell location

[#58381628]
Also retrieve size for new public stemcells

The size is uses to display download progress

[#58381628]
Add find? and has_stemcell? to PublicStemcells

For parity with PublicStemcellIndex

[#58381628]
Fix method argument order

[#58381628]
`bosh public stemcells` lists CI promoted stemcells

* Wired in PublicStemcells instead of PublicStemcellsIndex
* #58381628
Delete legacy public stemcell index

[#58381628]
Extract PublicStemcell to own file

Now that its legacy counterpart is gone

[#58381628]