(maint) Migrate ex to Pkg::Util::Execution

This commit migrates ex from 00_utils to a new module called
Pkg::Util::Execution. It also adds another method called success?, which
wraps the behavior of $?.success?, with the bonus of being more easily
stubbed/mocked in other tests. Some basic tests are included for ex. The
implementation of ex is moved from %x to `` to enable testability of the
method.
(maint) Update Pkg::Util::File for new Pkg::Util::Execution
(maint) Update 00_utils for Pkg::Util::Execution
(maint) Update Pkg::Util::File.mktemp to use Pkg::Util::Execution.ex instead of ``
(maint) Address order dependent test failures in Pkg::Util::Net

Because the net spec tests around ssh stub out ssh calls, there is no
guarantee that the $? object will be instantiated, which can cause tests
to fail if we try to get success? from nil. This commit updates the
tests to use the Pkg::Util::Execution.success? method, which is easily
stubbed out in tests. The implementation is also updates to use the same
method.
Merge pull request #315 from haus/maint/master/add_pkg_util_execution

(maint) Migrate ex to Pkg::Util::Execution
(maint) Migrate rsync_* into Pkg::Util::Net

This commit migrates the rsync_to and rsync_from methods from 00_utils
into Pkg::Util::Net. 00_utils now has deprecations for rsync_to and
rsync_from and will automatically dispatch to the new methods. The new
methods have an explicit parameter list, which was already being used in
all instances in packaging. As it is being moved from rake to pure ruby,
ex is used instead of sh in the invocation.
(maint) Use fully qualified paths for remote_ssh_cmd

Previously the remote_ssh_cmd utility shelled out to ssh when the fully
qualified path was available. This commit updates the implementation to
save the results of check tool and then use it. The tests are also
updated for this change and some stubs are made more specific.
(maint) Update all instances of rsync_to to Pkg::Util::Net.rsync_to
(maint) Update all instances of rsync_from to Pkg::Util::Net.rsync_from