(PUP-3680) Remove confusing convenience Hash[value-type]

In an attempt to be helpful, the type system offers a convenience
that if a Hash type is specified with one key, then this is taken
as being the type of the value (and the key type defaults to
Scalar).

In practice this proved to be confusing as it raises the question
about if it is the key type or the value type that is being
specified. Some users thought it was they key type, as that is
what they wanted control over, others thought it was the value type.

From a consistency standpoint (a Hash is a Collection), it could
be viewed as being a collection of Tuple[Key, Value], but implementing
that is not very helpful (it is just more to type). The best solution is
therefore to simply remove the convenience and require both Key and
Value type as a minimum. (This also removes the confusion over the error
if wanting to specify Hash[Value, 2,5] (which fails because 2 is not a
type). Now users have to specify the full type: Hash[Key, Value, 2, 5]
if they want to add min and max entries.
Merge pull request #3361 from hlindberg/PUP-3680_remove-hash-type-only-value-param-convenience

(PUP-3680) Remove confusing convenience Hash[value-type]
(maint) use el 6 master for Solaris agent testing

Prior to this commit, we were using Solaris masters to test agent
acceptance. This commit standardizes our master platform for Solaris
agent testing to match that of our Windows agent testing.
Merge pull request #3394 from rji/maint/stable/el6-masters-for-win-sol-agents

(maint) use el 6 master for Solaris agent testing
(maint) Add error message if GitURI is nil

Prior to this commit, if the options param was left out from the
ci:test:git rake task, it would only tell the user that nil was an
unrecognized task i.e.

`#<ArgumentError:  is not recognized.>`

This was not helpful in the case where that uri variable was nil.

This commit changes that by adding a ArgumentError check to see if that
git uri is nil.
(maint) Throw error if install urls are missing from final options

Prior to this commit, if the git urls were missing from the
final_options hash, the rake task would try to do a match on a nil
object and fail. This commit fixes that by raising an ArgumentError if a
url is nil.