All tags as a constraint item.

All tags as a constraint item.

Tags are defined to be a comma-separated list of values, so an example use
would be:

constraints: k1=v1 k2=v2 tags=a,b,c

Historically we have supported parsing constraints that used comma-separated
key,value pairs, e.g.

constraints: k1=v1,k2=v2,k3=v3

With the introduction of the comma-separated tags field, predictable parsing
of such a string becomes difficult.

This branch uses the following rules:
1) If 'tags' is included in the string then it must be of the first form.
2) If 'tags' are not present, comma-separted k,v pairs are acceptable but
marked as deprecated.

https://code.launchpad.net/~bac/charmworldlib/tag-constraints/+merge/232758

(do not edit description out of merge proposal)

[bac, 2014-08-29 19:28:55]

Please take a look.

[Marco Ceppi, 2014-09-03 14:53:49]

LGTM