(PUP-1060) Respect yum enable and disable repo flags

When a package resource is ensured => latest, the specific version
available will depend on what yum repositories are enabled and disabled.
Commit a4abf13d3 added the ability to pass arbitrary options to install
and update commands which allowed users to specify the --enablerepo and
--disablerepo options, but these flags would not be respected when the
latest package version was used. This meant that the latest version
found and the version that could be installed with the --enablerepo and
--disablerepo flags might differ, causing all sorts of bad things to
happen.

This commit resolves this issue by making the version query aware of
these flags. When a package checks for the latest version available, it
passes all repositories enabled and disabled to the update query.
Whenever an update query is made for the first time with a combination
of repositories that output is stored, so that only query for a given
combination of repositories is made.

Unfortunately, this change still relies on yumhelper to do the actual
querying. In the long run it would be good to use yum check-update
instead of the complex helper script so that we can actually test and
verify the code responsible for querying packages.