Support OpenStack Cloud Jenkins plugin upgrade

Version 2.47+ of the OpenStack Cloud plugin for Jenkins adds two new
SlaveOptions params, node_properties and config_drive. Failure to send
these params results in a failed request.

Replace method version_ge with testversion for plugin version
comparisons. Needed to enable deprecation and future plugin version
checking.

Refactor get_minion_options, replacing duplicated code blocks with if
checks.

Deprecate INSTANCE_MIN_CAPMAX config param, to be replaced with
INSTANCE_MIN, for configuring the minimum number of instances.

Issue: RELENG-2514
Signed-off-by: DW Talton <dtalton@contractor.linuxfoundation.org>
Change-Id: Ic8773bd4ef44ea09b5635c4a84d6452e29ad777c